Different Lies To Find The Spy

"I told Varys I was giving the princess to the Greyjoys. I told Littlefinger that I planned to wed her to Robin Arryn. I told no one that I was offering her to the Dornish, no one but you."

- Tyrion Lannister

Someone is a spy. But how to find them? This trope is about one solution. Tell multiple people different, but similar lies, and then see how the person the spy works for reacts. It may be worth noting that doing this doesn't inherently prove that the information leak is the work of an active spy - maybe they just have Loose Lips, and their spouse is the actual spy or something. In fiction, however, usually the leaker is a spy.

The Other Wiki calls this a "canary trap", after Tom Clancy's use of that term in his novel Patriot Games.

Compare Impostor-Exposing Test.

(Some entries here were copied from Canary_trap.)

Fan Works

 * In A Young Girl's Delinquency Record, Jenny runs ran a small ring of drug dealers, and told Stevie that Dr. Brinkmeyer was the ring's supplier, but also told an unnamed redhead of a different unspecified supplier; it's safe to assume that more people were told different sources as the ring's supplier. After she accuses Stevie of telling the police who the ring's supplier is, Stevie makes a run for it. Jenny interprets the running as a confirmation that Stevie was an informant for the police (instead of there being a coincidence). When Jenny gets home, her knuckles are bloody.

Film

 * A variation of the canary trap was used in the film Miami Vice, with various rendezvous dates leaked to different groups.
 * In the film The Heat starring Melissa McCarthy and Sandra Bullock, a canary trap is employed by a drug ring to decide the loyalty of a returning member who is detective Mullins' brother.

Literature

 * The canary trap was used in several of Tom Clancy's novels. Chronologically it first appears in Without Remorse, when a CIA official alters a report given to a senator, revealing an internal leak who was giving information to the KGB. Different versions of the report were given to other suspected leakers.
 * This trap was also used in Robert Littel's book The Company, and later in the TV miniseries with same name.
 * The technique also appeared in Irving Wallace's book The Word (1972), and in the 1985 spy novel London Match by Len Deighton.
 * In Han Solo at Stars' End, the first book in The Han Solo Adventures, the title character uses a canary trap to find a traitor and murderer among his passengers. He tells each that their target is a different planet, all false, knowing that the traitor would have learned the real destination when they killed the group's leader.

Live-Action TV

 * Tyrion Lannister determined that Pycelle works for Cersei this way in Game of Thrones, as shown in the page quote.
 * In addition to the example that provides the page quote, this plotline is also depicted in "What Is Dead May Never Die", during the second season of Game of Thrones.
 * The technique was used in the 1970s BBC television serial 1990.
 * In the third-season finale of The Mentalist, the characters use a canary trap (giving different hotel room numbers to different suspects) to uncover a mole within their agency.
 * A similar ruse to the one used in The Mentalist is used in the TV series Ashes to Ashes.

Web Comics

 * Girl Genius has Gil successfully catching one spy for a group trying to capture or kill Tarvek this way here.

Web Original

 * Done in Fenspace during the "Boskone War", in order to root out which group in the allies was leaking secrets to the enemy. Each group was told to rendezvous at a different location; when the enemy forces showed up early at one location to ambush the allies, the allies knew where the leak was.

Western Animation

 * In the Bob's Burgers episode "Tina Tailor Soldier Spy", Tina Belcher told different girls in her scout troop where a lead was for a place to sell cookies to find out which of them was spying for Troop 257.

Real Life

 * Who leaked the spoiler that in Star Trek II: The Wrath of Khan? Thanks to somebody making sure each script had a unique code - in essence, something different was told to each person involved - we know that it was.
 * The Electronic Frontier Foundation asks, with good reason, "Is Your Printer Spying On You?"
 * When distributing the film Broken to friends, Trent Reznor claims that he watermarked the tapes with dropouts at certain points so that he could identify if a leak would surface.