We're all familiar with the Face-Heel Turn and the Heel-Face Turn as well as all the sub tropes that go with them. However, there is the rare occasion when one character undergoes a Heel-Face Turn while another does a Face-Heel Turn almost simultaneously: that is the Face Heel Double Turn. This comes in many forms, particularly in a whodunnit mystery. For example, the Red Herring is revealed to be good all along while the real suspect is exposed. Or perhaps in a war the hardass Drill Sergeant Nasty isn't so nasty after all while a seemingly nice and innocent soldier turns out to be The Mole or The Big Bad. Of course, this trope isn't just restricted to finding out one character was good all along while the other was bad; it can refer to characters changing roles in a storyline.
The Trope Namer comes from Professional Wrestling, where two wrestlers will switch face and heel roles during an actual angle or match. It should be noted that it doesn't count if there are two faces and one turns heel or vice versa — both have to switch roles. Also note that despite the name, it needn't be confined to just two characters. The "double" part refers to two roles switching around.
When the main protagonist and antagonist do this, it's an Hourglass Plot. Not to be confused with a single character making two (or more) Turns in quick succession; that's a Heel-Face Revolving Door.
As a Betrayal Trope, there are naturally unmarked spoilers below.
I, Robot has a robot suspected of murdering his master by the cop investigating the case only for The Reveal to show it was actually VIKI, the seemingly benevolent super computer in the man's office, and the robot was innocent all along.
The Prestige has Angier portrayed in a sympathetic light after Borden inadvertently murders his wife. In their ongoing rivalry we root with Angier initially until he frames Borden for his own murder and intends to raise his daughter after her father is hanged. Then comes the reveal that Borden and Fallon are identical twins.
Snow White: A Tale of Terror has Claudia start out as warm and affectionate towards her new stepdaughter, offering Lilli gifts and hoping to be friends. Lilli rebuffs her and acts like a spoiled brat. Then when Claudia miscarries, Lilli tries to comfort her and apologizes for everything she has done, but her stepmother doesn't forgive and she tries to have Lilli killed and we start (also) rooting for Lilli for the rest of the story as she slowly matures and tries to mend her way and be a better authority figure.
In Spy Kids, Floop is supposed to be the villain, but near the end of the film he for some reason actually turns to the side of Juni and Carmen Cortez, while at the same time, his Dragon, Alexander Minion actually becomes the new Big Bad.
Actually, this is explained: Floop just wanted more money/ratings for his show, whereas Minion actually wanted to legitimately take over the world.
Harry Potter and the Prisoner of Azkaban follows the Red Herring example above. Sirius Black is, for most of the book, presented as an evil mass murderer who betrayed Harry's parents and murdered his childhood friend Peter Pettigrew. Then comes The Reveal that Peter betrayed Harry's parents and framed Sirius, and that the latter was in fact trying to protect him.
Goblet Of Fire - Cornelius Fudge (and by extension, the Ministry of Magic) becomes the enemy while Snape is outright stated to be on Dumbledore's side at the end.
Half Blood Prince - Malfoy goes from heel to face and Snape goes from face to heel, though Snape is revealed to have been good all along in the next book.
Both Catherine (the elder) and Heathcliff go through the Face Heel Revolving Door several times in Wuthering Heights that include bits where Catherine is a bitch for marrying Edgar and abandoning Heathcliff but then he's the bad guy for stirring up trouble and ruining her happy marriage while she's pregnant.
Coronation Street had an interesting case when Gail was mistakenly convicted for murdering her husband (he died naturally) and her son David was on her side (face) while her stepdaughter Tina believed Gail had actually killed her father (heel). After the story was over and she apologised to Gail, Tina began a relationship with Graeme (David's best friend) and became more sympathetic (face turn) while David opposed the relationship and tried to split them up (heel turn).
A variation happened with two entire dimensions in the Charmed season 6 finale where the sisters found an evil alternate dimension to their good one. They did too much good while in the evil dimension and that caused both dimensions to become extreme versions of their former selves. In the good dimension everyone was over cheery and smiling and people were shot for minor things such as using your phone at work. In the evil dimension it was the reverse where people got killed for saying "bless you" when someone sneezed.
Dark Willow in Buffy caused the previous big bads (Jonathan and Andrew) to become sympathetic as they were humans being punished by Willow for Tara being killed by their friend and Willow to become the new Big Bad.
Essentially happened with Angel and Drusilla before the show's continuity. Angel, as Angelus drove her mad and killed all her family before turning her into a vampire. However now he's good with a soul while she's evil and crazy.
The Angel episode "Inside Out" features a variation on the whole shoulder angel/devil thing when Darla (a villain for most of her time on the show) appeared in front of Connor when Cordelia (good but was possessed at the time) was trying to convince him to kill an innocent teenage girl. To make it more anvilicious, Darla was dressed in white while Cordelia was dressed completely in black.
The third season of Robin Hood has Isabella rejecting the Outlaws in favour of Prince John while Guy of Gisborne is gradually redeemed.
The Survivor Series 1988 where the Powers of Pain turned heel and Demolition turned face during their match because of the tactics they used.
The most well known instance of this happening is the famous "Stone Cold" Steve Austin vs. Bret Hart match at WrestleMania 13 where Bret went in as the face and ended up turning heel after the match and vice versa with Stone Cold.
A lesser known example would involve The Dudley Boys, who were heels, and the team of Test and Albert (T&A) along with their manager Trish Stratus, who were faces, reversing roles during their feud, with fans being very supportive of Trish getting powerbombed through a table at Backlash 2000.
An example that happened with an angle instead of a match (pardon the pun; this is going to involve a certain Olympic gold medalist). After the end of the Invasion angle, Stone Cold was part of the Alliance while Kurt Angle was The Mole for the WWF. The Raw episode after the end of the story had Kurt turn heel by being cocky and claiming responsibility for the Alliance getting taken care of while Stone Cold turned back face the same night.
A downplayed example happened with Lita and Trish Stratus. During their famous rivalry, Trish was heel and Lita was face but they both went down with injuries in the same year. Lita was still appearing on TV a while before Trish returned and turned heel in an unrelated storyline. When Trish returned, she became a face though the two didn't interact much. They did reignite their feud the next year only this time Trish was the face and Lita the heel.
This actually began before Trish went down with her injury. The fans turned against Lita after her affair with Edge became public knowledge. If you watch their in-ring segment from Raw on 4/18/2005, the fans are unmercifully chanting "You screwed Matt!" and "We want Matt!" at Lita, who was supposed to be the face. Trish tried to take the heat on herself, but it didn't work.
On Bound for Glory 10.10.10., Hulk Hogan, Jeff Jarrett, Jeff Hardy, and Eric Bischoff all turned heel together revealing themselves and Abyss to have conspired together to wrest control of TNA from Dixie Carter, naming their subsequent group Immortal. Suddenly the deception that Sting, Kevin Nash, and D'Angelo Dinero were talking about when they were rabble-rousing against Hogan and Eric Bischoff made perfect sense.
At the SHIMMER Volume 43 tapings face Mercedes Martinez had a match with heel Athena that ended in a double count-out and Martinez refused to restart the match. At the next volume she turned heel officially by attacking Athena with a steel chair and breaking her leg. Athena appeared as a face at subsequent SHIMMER events.
Happened during WWEs Payback PPV. Dolph Ziggler was facing Alberto Del Rio, heel and face respectively, for the World Heavyweight Championship.note Del Rio was invoking his rematch clause. Dolph had just returned to action after his concussion. During the match Del Rio repeatedly targeted Dolph's head. The fans started booing Del Rio and cheering for Dolph. In the end Del Rio won the World Heavyweight Championship. The next night on Raw the double turned was further implemented with Del Rio blaming the fans for not standing by his side, and after a match with CM Punk, in which he intentionally got counted out, was attacked by Ziggler, who would subsequently part ways with his stablemates Big E Langston and AJ Lee, who would stay together. By Friday, Del Rio was back to wrestling faces like Chris Jericho, John Cena, and his now-infamous rival Sheamus. Ziggler's very next match was against Antonio Cesaro, solidifying his turn.
Arguably, the Williams sisters in the Tekken series. Nina was always the nastier of the sisters as her endings show her stealing Anna's shoes, pointing a gun at her at their father's grave and taking a picture of Anna while she showered. In the fifth game Anna became a lot less sympathetic and Nina actually tried, but failed, to make peace with Anna.
Likewise, Kazuya and Heihachi zig zag through this all the time. In the first game Kazuya was the face as Heihachi had thrown him off the cliff as a child. At the end of the game he threw Heihachi off a cliff and took control of the Mishima Zaibatsu. Except he was a far worse leader than Heihachi was and the organisation became more corrupt, thus making Heihachi a face by default when he returned in Tekken 2. Though then he threw Kazuya into a volcano at the end of the game and became a heel again.
Played with in Final Fantasy X where the people following the Yevon religion were touted as good people while the Al Bhed race were "heathens". Then comes the reveal that the leaders of Yevon are corrupt people in charge of a Path of Inspiration and the Al Bhed come to help the protagonists.
A justified example in the sequel. Shuyin possesses Nooj before the game's story starts, making Nooj the one who shot Gippal, Baralai and Paine in the Den of Woe. During the middle of the game, Shuyin possessed Baralai instead and used his body to control the big bad machine underground, leaving Nooj free.
In X-Wing Alliance, The Mole on your ship reveals himself in the same campaign that an Imperial Officer defects and joins that ship.
Atlantis: The Lost Empire has the entire team turn heel on Milo to reveal that they're in it for the money. Then however most of the team turns face yet again to side with Milo while Rourke and Helga essentially become even more heelish killing the chief and kidnapping his daughter.