The villain approaches one of the good guys, often having captured them first. The good guy is then offered a deal: if he will help the villain by betraying his comrades, he will be amply rewarded with money, a high-ranking position in the villain's organization, or something else that would be attractive. He accepts the bargain, and keeps his end of it.
Of course, the villain has no intention of honoring his own part of the bargain. One reason is that no Card-Carrying Villain would want to share anything with a stooge who has outlived his usefulness. Another reason is that smart villains never trust a traitor, no matter which side he's working for — they can never be sure that their agent won't turn double agent.
So, the traitor gets the "reward" of being put to death or being reduced to menial slavery. Not such a pleasant outcome for him, is that? Frequently this is accompanied by a speech of withering contempt for treachery, which demonstrates that the villain is an honorable enemy or Worthy Opponent to some degree. In other cases, it could be more Pragmatic Villainy; as noted above, trusting a traitor is never a good idea. In a variation, the hero refuses to turn, and is rewarded and praised for his loyalty.
Sometimes it happens in reverse, where the good guys are approached with an offer by a would-be Turn Coat from the enemy, and invoke this trope to show their scorn for treachery — before or without even using him or his information. This can be a prime source of Values Dissonance with works created or set in feudally organized cultures, where loyalty placed much, much higher in the hierarchy of virtues than in modern western society. In these cases, what seems to the reader like a straight Mook-Face Turn will instead be met with an ostensibly deserved horrible fate.
One frequent variation has the villain show the good guy that he has his wife, and offers to release her from his prison in exchange for his cooperation. When it comes time to reward the traitor, the villain slyly gives him False Reassurance that she has indeed been "released", and that now it is time for him to join her.
In another variation, the villain (or in very old works, the hero, but this isn't done any more) is besieging a city or fortress. Someone leaves a side door (a sewer gate is a popular choice) open, and the bad guys storm in. But when the turncoat comes to the villain for his reward, he's promptly killed because that's what any traitor deserves. Can either mark the villain as a Complete Monster, or show that Even Evil Has Standards, depending on how it's played.
The one persistent exception to this trope if the reason for being a traitor was to indulge in their malicious urges that would be allowed under the new regime. While Greed, pragmatism, or cowardice won't save you from this trope, for some reason the Evil Overlord tends to trust people who betray their comrades out of hatred or cynicism.
Also, historically, Genre Savvy betrayers have always had two options open to them for averting this punishment. The first, if the betrayal was of a ruler, is to seize power as a de factoKlingon Promotion. Since some cultures consider this a legitimate method of succession, the new ruler will not be considered guilty of treason, though he may have to rule by fear to keep the former ruler's supporters from taking their revenge on him. The other method, if the betrayer lacks the ambition or power to seize the throne and hold it, is not to wait for the axe to fall but get the hell out of dodge. Notably, the latter method is especially recommended to anyone who has helped another betrayer achieve the former method: the new ruler all too often gets a taste for backstabbing minions as well as superiors, is just as Genre Savvy about this trope as his fellow conspirators, and will surely hate to be reminded that he owes his position to them.
Recurring problem for The Starscream, but a Defector from Decadence may face it too.
The end result of this is notTraitor Shot, though a Traitor Shot may be involved long before the fact, and the traitor will likely get shot.
In the Hellsing manga, the captain of a aircraft carrier, the HMS Invincible, turns it over to Millennium (turning the rest of the crew into ghouls in the process) in exchange for becoming a vampire. Rip Van Winkle arrives, congratulates him, informs him that his new orders are to "provide nutrients for the fish" and blows him away with her gun.
When this happens in OVA 4, she makes sure to point out that he "betrayed his True Companions" just for his own benefit.
In To Love-Ru, during Trouble Quest, almost all the characters are trapped in a VR game that seems to have Magical Girl Kyoko from Lala's favorite Show Within a Show as the Big Bad. Run, The Queen and her posse all agree to stop the progress of Rito and Lala's group in exchange for being sent home. Run ends up being chased by the pervert Principal (again) and Aya's would-be spell renders her own team topless. Their betrayal must have angered Yami, for she doesn't even punish Rito for gawking at them when this happens. In the end, not being with the main group has them all forgotten about when Kyoko is revealed as Lala's even more irresponsible sisters, testing Lala's circle of Earth friends. As a result, they are transported to the Amazon, where wackiness ensues.
During Vinland Saga, half of Askeladd's men turn traitor during a Stern Chase to escape Thorkell, and capture Askeladd. When Thorkell finally catch up to the waiting (and surrendering) traitors, he 'rewards' them by letting them pick up their own weapons again so they can die honourably and go to Valhalla when his men kill them. He leaves Askeladd alive.
The anime OVA of Ai no Kusabi has this combined with You Have Out Lived Your Usefulness. Iason has successfully used former Bison gang member Kirie to sell out and destroy the gang. When Kirie shows up to collect his reward money, he's instead taken away, Brainwashed and turned into an unthinking and obedient Pet.
In the Digimon movie X-Evolution, after WarGreymon X gathers a group of Digimon in an attempt to band them together for survival against the Knight Templar Royal Knights, Andromon reveals that he's already come into contact with them. When Omegamon arrives, he's one of those gunned down by the Jogressed Ultimate.
In DC'sVillains United #6, Cheshire, having leaked the location of the Secret Six's hideout to a Secret Society of Super-Villains death squad, attempts to leave the hideout to join them:
Cheshire: I'm coming out! I am unarmed! I'm one of you! I'm one of you! I am un— (shot by Deathstroke) Deathstroke: Sorry, Cheshire. We don't need any traitors in the society.
In Flash Gordon, after rewarding Sonja's treachery as promised, by marrying her and making her empress, Ming the Merciless immediately has her executed.
Happens in the Squadron Supreme limited series, when The Mink fatally stabs Foxfire after she betrays Nighthawk's rebels.
In the UK Sonic the Comic, after selling out the entire Chaotix Crew to the Metallix Empire, Nack the Weasel is told he'll "Get what he deserves". And he does, when the Metallix blast him, nearly killing him. Nack was actually Genre Savvy enough to expect this, and bring a Disruptor, but it didn't do him much good.
In The Jungle King the evil chancellor, seeking the throne, approaches the neighboring king for help after his last plan somehowfailed. The king agrees to help him, ostentatiously for a piece of the kingdom. After the chancellor leaves, the king asks one of his retainers to remind him to execute the chancellor after helping him. "Never trust a traitor."
In Legend of the Guardians: The Owls of Ga'Hoole, Allomere betrays the Guardians to Metalbeak, who soon after has him killed by bats. Allomere believed he would get to rule the Guardians' tree for his part, but Metalbeak told him "There can only be one king."
Films — Live-Action
The Mask: In a Deleted Scene, after Peggy sells Stanley/The Mask to Tyrell and his men, the first thing Tyrell does after putting the Mask of Loki on is toss Peggy into a printing press, killing her.
In Inglourious Basterds, the Allies accept Hans Landa's offer to betray Hitler in return for protection after the war. Aldo Raine is furious that the Allies uphold their end of the bargain, but manages to get one last shot at Landa by killing his minion and carving a Swastika into his forehead, marking him for life as a Nazi.
In the original Battlestar Galactica movie, the Cylons beheaded Baltar after he betrayed his fellow humans.
Serenity. Mr. Universe reluctantly cooperates with the Operative by luring the Serenity into an Alliance trap. Afterwards he turns to the Operative and begins an angry rant, only for the Operative to run Mr Universe through on his sword rather than allow any chance of the truth coming out. Bonus points because the traitor was demanding his thirty pieces of silver. He knew that one way or another, he didn't have much to look forward to after what he'd done.
In Ran two retainers help defeat their master, Hidetora. Hidetora's son rewards them as they agreed, however he then explains that he can't very well have retainers who obviously disregard loyalty to their master, and kicks them out. Later on they wander too close to one of Hidetora's loyal followers and get chased down and killed.
Superman II. Lex Luthor betrays the human race by allying with the Kryptonian super villains and leading them to Lois Lane so they can find Superman. After he does this General Zod orders Non to murder him, and he's only saved by the arrival of Superman.
Roach from Demon Knight sells out his friends to the demon leader and his horde, in exchange for being spared. Not surprisingly, the head demon informs him that he lied and promptly has his horde devour him.
In the HammerFu Manchu movie series, Fu rewards just about everyone who helps him by smiling, thanking them, then having them dragged away to be imprisoned or executed. One wonders how he manages to get anyone to help him at all by the time the last movie in the series rolls around.
In Sucker Punch, Blondie tells Blue about the girls' plan to escape, but only because she didn't want her friends to die. Blue praises her, at first, then replies that he doesn't like snitches. She's quickly dispatched with a bullet to the head.
Snatch: Brick Top's Establishing Character Moment has him 'disposing' of someone who's apparently betrayed him in some manner or other (we're never explained what) before having the man's lieutenant, who gave him the tip, 'disposed of' in the same manner while explaining he's "got no time for grasses".
This happens to Nash, Cobb's original architect in Inception, who betrayed Cobb and sold him out to Saito. Saito originally offers Cobb a gun to deal with it personally, but Cobb isn't willing to kill. Saito then leaves him to the mercy of Cobol Engineering, who would inevitably hunt him down and kill him when they catch him.
In Sword of Sherwood Forest, the Sheriff makes this offer to one of Robin Hood's men; promising him a free pardon. After he gets the information, the Sheriff has him shot and then orders a pardon drawn up for him.
In the film Immortals, Lysander does a Face-Heel Turn since he fears Hyperion's forces cannot be stopped. Hyperion agrees to take him in, but orders his guards to physically scar his face as well as neuter him via giant mallet, since he feels Lysander shouldn't get preferential treatment for switching sides the way he did, nor does he want the traitor to spread his seed by having kids.
In The Patriot, when Tavington rounds up an entire town suspected of aiding Martin's soldiers, he offers them forgiveness if they give up any relevant information. One of the townspeople ends up talking, but Tavington has the entire town killed anyways, saying that they can get their forgiveness from God.
In a 1979 Romanian biopic of Vlad Dracula, a battle with a rival prince is averted when he's killed by his own captain. When Vlad orders the assassin executed (with his own murder weapon), he points out that Vlad would have slain his rival anyway. Vlad counters that he never swore loyalty to him.
In Wrath of the Titans, Perseus warns everybody not to pray to Ares, since a god can hear and locate anybody who prays to them and Ares is their enemy. Eventually, Korrina gives in to fear and prays to Ares, thinking he will save her. Ares teleports to the heroes' location and starts slaughtering everybody. When Korrina reveals herself as the person who prayed to him, Ares kills her without a second thought.
Discussed and wiggled around in Hard Boiled, when Alan (secretly an undercover cop named Tony) is in the process of selling out mob boss Mr. Chiu to the up-and-comer Johnny Wong. He insists to Wong that he's not a traitor and will be loyal to Chiu until Chiu is dead, and then helps to make that the case. Wong is entirely okay with this and keeps Alan around, but his right-hand man, Mad Dog, is unimpressed with the treason.
In the Planescapeverse, the githzerai race, which is much devoted to examples in history and folklore, uses the story of Vilquar to describe the foolishness of betrayal in general. Once, when the Mind Flayers were still holding their race in slavery, Vilquar tried to get special treatment by selling out the rebellion. They tricked him into thinking it had disbanded, and when he went to claim his reward, Vilquar's master ate his brain.
While the convicts of the Penal Legions of the Imperium in Warhammer 40,000's crimes vary from more standard crimes such as murder to heresy and apostasy, the Imperium clearly sees them as traitors to the Emperor — fit only as cannon fodder. Subverted on some occasions since it is possible for Legionnaires to be pardoned for performing a particularly meritorious act.
This happens to Parolles in All's Well That Ends Well — although his captors were actually his comrades playing a trick on him.
In the stage version of Bugsy Malone, Shady gives Fat Sam information that will lead his men into a trap; he then collects his money from Dandy Dan only to be killed (splurged) while walking away. Dandy Dan takes back his money, commenting he can't stand traitors.
In The Thwarting of Baron Bolligrew, the Baron hires Doctor Moloch to poison the dragon that rules half the island. When the Baron attempts to pay his fee with chocolate money, Moloch goes to the dragon's cave and tells it of the plot (omitting his own part). The dragon, having thanked Moloch for the information, promptly tempts him into its cave with promises of financial reward and eats him.
In Girl Genius, Dr. Beetle, the much beloved ruler of Beetleburg, dies as a result of Silas Merlot's unnecessarily dramatic actions. Merlot attempts to toady up to Baron Wulfenbach and formulate a plan to hide Dr. Beetle's death—whereupon the Baron commands that Dr. Beetle be given a funeral with highest honors, the exact details of his death hidden from the public, and, just to illustrate to Merlot how hard he's fucked up, Merlot is put in charge of Beetleburg and the University. Merlot, having never much liked our protagonist Agatha, expels her on the spot for sheer petty spite. Later, a team of Wulfenbach's cryptographers decode Dr. Beetle's encrypted notes, revealing Agatha's true identity to Merlot, who begins a frantic search for her, which fails (because she's already on Castle Wulfenbach). Merlot thinks that if Wulfenbach found out who Merlot let slip through his fingers, it would be curtains... so he destroys all evidence — labs, record halls and the cryptographers — in a fire. Wulfenbach discovers it another way, finds out about Merlot's attempts to cover his butt and so he sends him to Castle Heterodyne..
In Sluggy Freelance, the future Lord Horribus is set to do this to his informant Amospia, who gave the demons the key to the city so that she and her lover could escape. The Asps accidentally kill Amospia's lover, then are accidentally fused to her when she is turned into a snake demon.
In the first Wing Commander Academy episode, "Red and Blue", the human technician who betrayed the Terran Confederation was asked by the Kilrathi captain he ran to with the stolen information why the human had betrayed his own kind. In a subversion, the captain spaces the human not for the treason, but the reason for it not being "noble" by Kilrathi standards.
A mild version occurs in an episode of The Simpsons. Bart pulled a prank at church by switching the opening hymn with "In-A-Gadda-Da-Vida". Milhouse ends up ratting him out and is praised by Rev. Lovejoy for it, who then takes Bart away from punishment...and drags Milhouse along, too, saying, "You too, snitchy."
In Gargoyles, this happens when Demona betrays Macbeth to Canmore. After Canmore "kills" Macbeth and Demona, he says, "She betrayed Macbeth; it was only a matter of time before she would have betrayed us. It's a good thing we had the rest of her clan destroyed as well. Her kind was an abomination; they did not deserve to live!"
In Skeleton Warriors, Baron Dark frequently rewarded people who betrayed the rebels by turning them into more Skeleton Warriors. Since the transformation burned all of the goodness out of a subject, it effectively turned them into a Black Shirt and partially falls under the exception mentioned near the end of the trope description.
Played with in the Justice League Unlimited finale. In the aftermath of an Enemy Civil War, Luthor's side has beaten Grodd's and Luthor asks if any of them can give a reason they shouldn't continue following Grodd. Killer Frost, one of Grodd's cabal, steps forward, turns around and immediately freezes all the others on her side. This even unnerves the villains Luthor's side.
Luthor: Killer Frost...you've got a future. Get rid of the rest.