Perhaps you need to smuggle some recognizable people into a base, or smuggle some friends out of a hostile situation. Perhaps the two of you have just been caught by your enemies, and are trying a bluff. Time for the Trojan Prisoner trick.
In the simple version, some of the protagonists pretend to be enemy mooks, with the others posing as their prisoners or slaves. Quite often, the main hero gets to play the captive, being the most recognisable, but if the mooks have face-concealing outfits, it's the least recognisable member of the group who gets tied up.
In the other version, the fake guard is someone the enemy thinks is on their side, e.g The Mole, a reformed villain, or a Loveable Rogue. They swagger into the enemy camp, show off their captive, then surreptitiously help them escape, while doing a little espionage on the side. The fake guard doesn't always bother telling the hero the plan in advance either; the act is much more convincing if the hero thinks it's real.
This can be used to play up the relationship between the characters, allowing the captor to temporarily treat the captives like dirt, or to express cruel opinions that hit a bit too close to the truth. If the disguise relies upon actually restricting the captives significantly, this can play off characters' mistrust of the fake captor, especially one who is very close to the enemy. However, it's pretty rare for the fake captivity to become real.
Occasionally, this trick is proposed offscreen, leading the viewer to think that a major character pulled a Face Heel Turn.
If they are physically bound, this can lead to a Chained Heat or fighting With My Hands Tied. Compare I Surrender, Suckers, and cases where anyone should be able to see through overlap with The Guards Must Be Crazy. The Play Along Prisoner may allow themself to be tortured before breaking loose. Compare Sheep In Wolf's Clothing, where this applies to The Virus, and with Trojan Horse, which also gets the hero into an enemy base, but without them knowing anyone has crossed their lines. Compare Bavarian Fire Drill, which relies on bluffing rather than a convincing disguise. Contrast Disguised Hostage Gambit, where real villains with real hostages dress the hostages up as villains to fool The Cavalry.
Not to be confused with the similar, but distinct, Alone With Prisoner Ploy. That's when a reformed bad guy or good guy on the inside asks to be alone with an actual prisoner in order to help him/her.
In One Piece, during the Impel Down riot, Mr.2 does this with Buggy and Mr. 3. They get past Magellan and then manage to reach Level 5 (in order to save a captured and poisoned Luffy) thanks to Mr.2's ability to change his aspect. He disguises as Hannyabal and then takes the other two with him as his prisoners.
In Dynamo 5, a government agent pulls this on the main characters, without telling them, leading them to believe he's turned evil.
In The DCU, Batman once infiltrated Belle Reve prison, home of the the Suicide Squad, by posing as criminal 'Matches' Malone and arranging for Commissioner Gordon to have Malone held there while being transferred.
In the Doctor Who comic "The Futurists" in Doctor Who Magazine (from the collection The Betrothal of Sontar) this is used to infiltrate an ancient Roman military camp. Lampshaded when the Doctor remarks that it's a tired old trick, but there had to be a time when it was new enough to work.
As an homage to A New Hope's use below, this was used in Allronix's Knights of the Old RepublicFan FicDestiny's Pawn, as Carth attempts to bluff his way through a Sith base with Zaalbar as a "prisoner." Subverted, as the receptionist on duty doesn't buy it for a second.
In the Goblin Valley, Ringo has to pretend to be a human slave being led by George, who's become a goblin.
At the climax, Paul has shaken off mind control but pretends to still be under the influence to gain entry into the warehouse where the Vasyn is being kept. George is Dressing as the Enemy (he becomes the woman Bayanis, who is in charge of Paul) and goes in with him. John and Ringo have to think of another way in.
In Star Wars: A New Hope, where Han and Luke pretend to be transporting their Wookiee "prisoner," Chewbacca. And Leia recycled the trick for the third movie.
A New Hope is also a subversion, though, as the one manning the detention center has some suspicion towards Chewbacca, forcing them to abandon the trick and orchestrate a "one-man prison revolt" to get rid of the guards and the security footage.
The Rebellion repeated the trick in Return Of The Jedi with Leia infiltrating Jabba's palace by posing as a bounty hunter and bringing Chewbacca in; not to mention letting herself be captured. (That's right, it was intentional. None of them thought they could ever sneak out of the place. The whole point of the overall plan was to fool Jabba into putting Luke in a situation where R2D2 could deliver the lightsaber he had hidden inside him, and then make a surprise attack, and in the end, it worked perfectly.)
This plan required first that R 2 D 2 and C 3 PO be given to Jabba as gifts of good faith. Then Leia (in disguise) delivers Chewbacca, frees Han from the Carbonite, and is captured herself. Then Luke walks in, demands the release of his friends, and is captured (after a fight). Once they have thus gotten the entire crew together in one place, and out of Jabba's palace (for the execution), the Big Damn Jailbreak ensues. The only person who had to do a conventional infiltration was Lando, who evidently just signed up for a job opening as a mook.
Subverted in Dark Empire, where Palpatine abducts Luke, Luke hatches a plan to pretend to be Palpatine's apprentice and then kill him, but in the end, Luke himself goes over to the Dark Side only to be saved by Leia. In the end, Han kills Palpatine.
This is parodied in Twisted Toyfare Theater, where every plan the group has seems to involve putting Chewbacca in binders for some reason.
In The Mask, Jim Carrey's character gets a police officer to do this for him, at gunpoint.
In Star Trek Nemesis, Data uses this trick to get Picard onto the Reman warship Scimitar while pretending to be his own Evil Twin.
Both Ocean's Twelve and Ocean's Thirteen featured one of Linus Caldwell's parents stepping in to pull this off — his mom in Twelve, his dad in Thirteen. Poor Linus. How can you be an effective high-stakes thief when your parents won't stop looking over your shoulder?
Rusty does the same to Basher in Ocean's Eleven, posing as an FBI agent to take him into custody before the LAPD can take him.
In The Proposition, The Burns Gang infiltrates the police station by having Two-Bob put on full traditional Aboriginal dress and war paint while Sam and Arthur steal police uniforms and drag him into town as their prisoner.
Blood Diamond, although it lasts about twenty seconds, (just long enough for the soldiers to lower their guard and the "prisoner" to shoot them) and is done to cross a bridge.
Played straight in Windtalkers when Ben Yahzee dresses up as a Japanese soldier and takes his "captive" Joe Enders into a Japanese camp in order to gain access to a working radio.
In Face Off, this kicks off the plot, where the good guy takes the bad guy's face to get some information. This would have worked out if the bad guy hadn't woken from his coma and taken the good guy's face.
Done in Monsters vs. Aliens, with the other monsters wearing the clone outfits and escorting Ginormica.
In Top Secret!, Resistance members Chocolate Mousse and Deja Vu wear German army uniforms and march Nick Rivers ahead of them at gunpoint in order to infiltrate Fleurgendorf prison. There are two jokes: Chocolate Mousse is black (and all of the German soldiers are white), and as they're goosestepping, their boots fly off.
In The A-Team, Murdock is disguised as the General by wearing a bag over his head, and when Pike shoots him, it appears that he has died. Actually, it was ketchup packets and explosive squibs.
In Force 10 From Navarone, Mallory and Barnsby get back into the Chetnik camp they had just escaped from by getting two partisans to disguise themselves as guards (The guards in question being two with allegedly burned faces covered with bandages, so facial recognition isn't an issue) and take them back in through the front gate as recaptured prisoners. They then rescue their still-captured medic and explosives expert (And the explosives expert's suitcase full of explosives).
In the 2010 French thriller Point Blank, a fugitive pretends to be a cop and leads his ally (also a fugitive) into a police station in handcuffs. This is the only way for them to enter the police station and retrieve a piece of exculpatory evidence without attracting notice.
In The Dark Knight Rises, Bane and two of his mercenaries let themselves get captured so he can find out exactly who Dr. Pavel made a deal with instead of him. That soldier who informs the CIA agent that the hooded prisoners worked for Bane? It might take a second viewing of the film to realize that he is Bane's right-hand sniper, Barsad, posing as a Uzbekistan militant.
Later, when Bruce returns to Gotham, this is the method through which he gets to Fox, who can help him reach his backup Batsuit. First, he enlists Selina Kyle by appealing to her better nature and offering her the Clean Slate program (it is hinted that a Trojan Prisoner ploy will be used when Bruce tells her "I need you to find out where they're holding him [Fox], then take me in"). The steps after that are simple: Bruce lets himself get captured by Bane's men, who put a bag over his head and take him to the holding tank where Lucius Fox and Miranda Tate are being held. After he is deposited, Selina comes down and tells the mercenaries that Bane wants Bruce and Fox isolated from the others. They are led upstairs with a few mercenaries, and once out of sight from anyone else, she uses her Combat Stilettos to knock out the mercenaries and unlocks Fox's handcuffs:
Lucius Fox: I like your new girlfriend, Mr. Wayne!
Selina Kyle: He should be so lucky.
In G.I. Joe: Retaliation, Storm Shadow disguises himself as Snake-Eyes and allows himself to be captured so he will be transported to the prison where Cobra Commander and Destro are being held.
Treasure Island: Long John Silver pulls this with Jim, who'd been genuinely captured by Silver and the other pirates earlier. Silver's practical reason for keeping Jim alive is that he's his best chance to escape the gallows if things go south, as Silver suspects they might, and an extra gun hand against the pirates who'll inevitably turn on them once that happens. However, it's never entirely clear whether Silver would have kept his word to keep Jim alive if things had gone according to plan...
The Black Jewels series uses this to great effect in the third novel, when Daemon pretends to betray and capture Surreal.
American Gods: Czernobog and Mr. Nancy dress as police officers to get Shadow out of prison.
In the first trilogy of the Dragonlance Saga the good guys try to do this and fail miserably when they are captured because they lack the proper paperwork. This rather original subversion is somewhat lampshaded when the hero is frantically trying to think of a way out of the mess and realize that of all the things that could have gone wrong with their plan, no one considered the idea that they would be suspected of being deserters.
Hero: ...Enough of this talking, harharhar. [Beats up guard] I runs out of ideas after a while.
Chase, of the Sword of Truth series, does this using his adopted daughter as the captive, in order to make a rescue attempt. Coincidentally, two other groups of characters use similar disguises to perform the exact same rescue, each of their own volition. After they meet up with each other, they make their way out with the rescuees playing the captives.
The Scarlet Pimpernel and the French Aristocracy whom he was trying to rescue often wore disguises to get past revolutionary-held borders and checkpoints. In one particularly brilliant scheme, he dressed himself and a group of rescuees as revolutionary guardsmen, who approached a border checkpoint, claiming to be after a suspicious cart that had just gone through it. The Pimpernel and his group were let through, and the scheme remained undiscovered — until a few minutes later when the real guards showed up.
Ur-Example: Sinon in The Aeneid pulls this on (you guessed it) the Trojans to try to get them to bring the horse into the city. You know that thing about "beware Greeks bearing gifts?" that was in context, about him specifically.
In the X-Wing Series novels, part of the plan to retake Coruscant from the Empire is to take dangerous criminals, a significant part of the intergalactic crime syndicate Black Sun, from the prison world Kessel, then smuggle them to Coruscant where they will cause havok and distract Imperial forces. Unfortunately, some of those criminals still have Imperial ties.
In the comics, very soon after he has defected to the Rebellion Soontir Fel darkly hints that he's a Fake Defector to get intel out of a reluctant Imperial captive.
"Side Trip", a novella written by both Timothy Zahn and Michael Stackpole, has Thrawn-in-Mandalorian-armor pull a blaster on Corran and his father after guiding them into a mutual enemy's clutches. Thrawn, assumed to be a bounty hunter going with the money, exchanges threats with Corran, telling him that he'll "seek you out and take care of you personally" and that he would be the only thing between Corran and freedom, even grabbing the cell bars and shaking them after Corran and his father are imprisoned. After Thrawn and the mutual enemy have left, Corran's father shows his son that the bar-shaking move was a cover, letting Thrawn stick a molecular stiletto - think tiny lightsaber with a very fragile blade - on the bar. "Taking care of you personally" meant that when they escaped and got back to him, Thrawn would be in a better tactical position to start shooting, and they'd be on the same side.
The Wraiths once pull a weird version with actual prisoners. The plan goes like this: Wraiths start a bar fight with Imperial pilots; more Wraiths show up dressed as military police and arrest all the fighters; Imperials get knocked out on the way back to the stockade, and the Wraiths from the bar change into police uniform too; all Wraiths infiltrate the base as fake guards with real (unconscious) prisoners. Mind, they got the idea because, earlier in the book, agents of Warlord Zsinj tried to do this to them...and failed when one of the Wraiths saw through it.
In Warrior Cats a group of ShadowClan elders agree to help the ThunderClan warriors recover the kits ShadowClan had stolen. They drag former ShadowClan outcast Yellowfang into the camp and present her to their leader as their prisoner as they sneak the ThunderClan warriors into the camp.
Alvin Fog and Mark Scrapton do this in order to get access to the prison where 'Handsome Phil' Foote is being held in The Justice of Company Z by J.T. Edson.
A large-scale example in the Belisarius Series: In order to capture a major enemy stronghold, Belisarius and most of his army are "taken prisoner" after being "defeated in a battle". They are escorted into the stronghold by a group of a couple thousand soldiers who used to be on the enemy's side, before defecting en masse in a prior novel.
In the second novel, Belisarius has had Prince Eon assume the role of ridiculously oversexed ladies man who has to have a harem of prostitutes/slaves in his presence to satisfy his urges. The Malwa they are traveling with thus never notice when there's an extra one that's appeared out of nowhere: the escaped Princess Shakuntala.
Live Action TV
Used by Alex in LOST, and lampshaded by Sawyer: "Don't get mad at me because you fell for the Wookiee Prisoner gag."
Firefly, "The Train Job", Inara gets Mal and Zoe out of holding by pretending they're escaped indentured servants.
Slightly subverted in that the sheriff is obviously suspicious of this but not enough to stop them. He also believes he has judged Mal correctly when he sets an ambush, expecting him to return the stolen loot (which turns out to be desperately-needed medical supplies). He lets Mal go after getting the loot back.
Mission: Impossible has done this several times, often to get a member of their team into a prison, such as in "Old Man Out", "Trial By Fury" and "The Test Case".
In Red Dwarf, the Cat and Kochanski dress up as Gelfs (with Lister as himself) in order to get into a Simulant's ship.
In Spike's introductory episode on Buffy the Vampire Slayer, Angel tries this with Xander as the prisoner, using Enforced Method Acting to coax realistic prisoner behavior out of him. It doesn't work as Spike knows Angel too well and thus knows he's faking it.
This Trope appears in a Season 3 episode in which Angel's soul is apparently removed by a sorcerer, thus allowing Angel and Faith to kidnap Buffy and in reality allowing Angel and Buffy to learn of the Mayor's plans for the ascension. Since this is quite drawn out, it might actually count as a reverse interrogation instead.
This is how Michael Weston gets to a fugitive on the lam in the Burn Notice episode "Friendly Fire." Michael plays the prisoner.
The voiceover even came close to calling the trope by name: "The ultimate Trojan horse is a shackled prisoner."
Londo attempts this with G'Kar against Cartagia in Babylon 5. Starts to be subverted when Cartagia replaces G'Kar's rigged-to-break chains with real ones on a whim, but G'Kar breaks them anyway.
Used to get Byers and Bond out of prison in The Lone Gunmen after they went in trying to prove a prisoner's innocence only to find out that the guy's actually guilty, but that another prisoner has been framed, and freeing him.
An exceptionally brief version appears in Farscape, where D'argo and Sikozu, in the midst of a riot between her species and the Charrans, progress by going up to a guard pretending that he captured her, and immediately punching him in the face. Then going to the next guard and doing the exact same thing, word for word.
Used in Chapter 15 of Red vs. Blue: Reconstruction, where Church poses as Agent Washington's prisoner so they can get past they at the A.I storage facility. It fails when one guard gets suspicious and decides to report it to his superiors, leading to a shoot-out instead.
Used in "Bee in the City", a Transformers convention script-reading starring the cast of Transformers Animated. Flareup has to sneak Bumblebee and Beast Wars Megatro - uh, I mean, "Joe" into Shockwave's lab to rescue Sari and Optimus. She does so by claiming they're Primes, who aren't allowed in Axiom Nexus. There's even a "cell-block one-one-three-eight" reference (which the guard doesn't get).
Used in Assassins Creed Brotherhood, by faking the capture and delivery of Bartolomeo d'Alviano to the French, in order for Ezio to get close and assassinate the Baron de Valois. Bartolomeo's captors are all his own troops (and Ezio) wearing stolen French uniforms.
Assassins Creed III has this as a gameplay mechanic. Connor can summon Assassins disguised as Redcoats to take him "prisoner" and march him into heavily fortified locations.
A villainous example: The intro of Batman Arkham Asylum has Batman dragging The Joker off to Arkham after thwarting a hostage situation that involved the Mayor that was instigated by the latter, noting that it was suspiciously easy this time around. Turns out, he's right and it was all part of the Joker's plan to take over the madhouse. Turns out that when you take an insane person to the asylum, you're just taking him home.
A variant is used in Dragon Age II during Isabela's personal quest in act 3. Hawke turns her over to one of Castillon's agents, then tracks the agent back to Castillon's base.
In Mass Effect 3, Shepard pretends to be held prisoner by Narl in order to negotiate the Blood Pack joining the mercenary army that Aria T'Loak is building. Shepard also acts as a distraction to allow The Starscream to launch their planned coup.
A rather convoluted example in Metal Gear Solid 2 Sons Of Liberty. Snake and Olga teamed up and then apparently betrayed Raiden near the entrance to Arsenal Gear, and subdued him, captured and delivered him to Solidus's men. The betrayal was actually faked in order to lessen security onboard Arsenal Gear, although they never told Raiden before doing it, presumably in order to sell the act. This understandably left Raiden really ticked off at Snake when he met up with him later.
One mission in Guild Wars Nightfall involves Dressing as the Enemy to infiltrate Varesh Ossa's base. If you bring your centaur companion, who can't ("You may be able to dress as Kournans, two-legs, but what am I supposed to be, your mascot?"), guess what you do with him. (Complete with dialogue straight out of Star Wars!)
In Tales Of Symphonia, the party does this to infiltrate the Asgard Ranch. And again in Welgaia
And once again in the sequel to infiltrate the Vanguard. Subverted in that though the mooks fall for it, Alice isn't fooled and throws all of them in prison. Except they still get it to work, shutting off the power and escaping in under a minute
Happens in Tears To Tiara with Octavia, a former imperial officer, with Morgan as the fake prisoner. It would have worked, if it weren't for the fact that the unit that Octavia associated herself with was known to have been destroyed a long time ago.
Futurama "A Clone of My Own", Fry is brought into the "Near Death Star" as an escaped prisoner.
Buzz Lightyear of Star Command almost goes through with it, with the Commander disguised as a bounty hunter leading Buzz's captured squad away. Unfortunately, the Mole they're secretly rescuing pops out from stowaway too early.
Brain: Oh yeah? Sweet freedom! Emperor Zurg can kiss my big, fat cerebellum. Oh... we're not at Star Command yet... are we?
In the Teen Titans episode "Titans Together", Jericho takes possession of Cinderblock and pretends that Pantha, Mas and Herald are his captives. He botches it when he speaks through Cinderblock, who up to this point would only grunt and roar.
When Spongebob is transported to Ye Olde Bikini Bottom, the group infiltrates the evil wizard's castle with the recently-befriended Black Knight (Sandy) pretending to have captured Spongebob, Patrick, and Squidward. Despite knowing that this is a trick, Spongebob reacts with genuine fear when Sandy relates all the various horrible ways she plans to have them tortured.
Combined with I Surrender, Suckers in Beast Wars; In order to combat the return of the G1 Starscream (it's complicated), the Maximals pretend to surrender themselves to the Decepticon, in exchange for allowing one of their (exaggeratedly) injured comrades to use the repair bay inside their commandeered base. Starscream buys it, and locks the Maximal and their leader Optimus in the brig as leverage while ordering the rest to attack the Predacons. Turns out, though, that's exactly what the Maximals wanted, as it puts the two "prisoners" in a perfect position to retake the base.
Similarly, Rattrap's defection. It was a ploy to find out how the Predacons were intercepting Maximal communications so easily. Turns out they had stolen a Maximal decoder chip, which Rattrap was now in a perfect position to recover.
And in the Season 1 episode Imprisoned, they visit an Earth village that was taken over by the Fire Nation. Katara pretends to be an Earthbender in order to be taken to the prison ship in which the Fire Nation put all of the other Earthbenders, in order to free one of their friends who was captured.
And in "The Runaway" episode: Katara pretends to turn Toph in to the authorities to collect the sizable reward money, with the intention that Toph will simply metalbend her way out of jail. It doesn't exactly go as planned.
Awsomely subverted in Titan A.E. when Stith and Preed try to infiltrate a colony with this trope.
Guard: (Raises his weapon, pointing it at Preed) You're lying! He's not a slave and you're not traders. He doesn't carry himself like a slave! Look at the way he stands... probably ex-military. Akrennian traders always threaten before they ask a favor, it's tradition. (to Stith) And YOUR robes are made out of bedspreads.
And then the guard sees their Plan B. Kicked in the face by a Mantrin. This entire bit was brought to you by Joss Whedon.
In the Kim Possible episode "Two To Tutor", the "police helicopter" that picks up Shego and Seņor Senior Junior turns out to be a fake piloted by Seņor Senior Senior.
In the Aladdin episode "A Sultan Worth His Salt", Aladdin allows himself to be captured by the Galafems during a rescue mission to save Jasmine. While the Galafem queen and her troops interrogate Aladdin, Genie and the Sultan infiltrate the island, tie up and gag the queen's sentries, and ultimately save the day.
Used heavily in the Young Justice episode "Terrors", where Superboy and Miss Martian disguise themselves as supervillains and allow themselves to be "arrested" by the Justice League. While in Belle Reve prison, they foil an attempted breakout and save the day.
A similar escape happened at Colditz POW camp. The Allied prisoners were quite adept at making convincing fake guard uniforms, but the process was slow. It was noticed that a storeroom in the outer courtyard of the castle was occasionally visited by work details from another camp under heavy guard. After digging a quick tunnel to the storeroom and acquiring some Polish NCO uniforms eight prisoners were able to walk straight out of the camp following a shift change, while using up only two of the precious Guard disguises.
The Dutch resistance freed 44 prisoners from Leeuwarden prison during the German occupation in 1944 by sending five men into the prison using this trope.