The Commies Made Me Do It

A character -- more often than not female -- is revealed to be a traitor.

She however has a "Get Out of Jail Free" Card. Her boyfriend (or, if she's the romantic interest, her brother) has been arrested by the Secret Police in Commie Land and unless she helps them, they'll kill him.

Compare to I Have Your Wife.

Comic Books

 * In a Marvel What If? where the Submariner joined the Fantasic Four and married Sue, Reed Richards hired a lab assistant whose family was being held hostage by Doctor Doom. (She does help foil Doctor Doom's plan and save Reed's life before he married her.)
 * In the 1940's Wonder Woman series, a villainness Paula von Gunther who worked for the Nazis was revealed as doing so because they had her daughter captive. (In the comics she was a willing accomplice, until her Heel Face Turn)

Film

 * Red Dawn features a literal implementation of the trope: the Wolverines are betrayed by one of their own after the Commies threaten his father. Subverted somewhat in that it doesn't work as a "Get Out of Jail Free" Card.

Literature

 * Ian Fleming did it in Casino Royale.
 * And this trope was kept in the film version.
 * Although Quantum of Solace adds an interesting twist by revealing
 * In Dune the character captured by the Harkonnen. For this reason he betrays the Atreides (his loyalty conditioning would make this otherwise impossible, but I guess his loyalty to his wife is able to trump even that).
 * As a bit of a subversion,
 * In The Scarlet Pimpernel, Lady Marguerite Blakeney (an intelligent, beautiful, sophisticated yet naive young woman who is unhappy in her marriage) betrays the title character to the evil Citizen Chauvelin, because Chauvelin has dirt on her brother. Of course, her foppish husband,.
 * And she
 * In James Swallow's Warhammer 40000 novel Faith & Fire, the psyker Vaun escapes because many crew members on the ship have been convinced that his cell really holds someone they love. One, being interrogated, weeps about his beautiful daughter, and the prison warden says he has no daughter. On being asked what his daughter's name is, he dies.
 * This being Warhammer 40k, though, it wouldn't have helped even if it were true.
 * Later in the Harry Potter series, the Malfoy family. In Deathly Hallows, Narcissa Malfoy falsely announces to the Death Eaters that in exchange for knowing that Draco is still alive.
 * Xenophilius Lovegood because his daughter Luna was kidnapped by the Death Eaters.
 * Many people claim this anyway in Harry Potter when Voldemort is in power. Plenty are genuinely being blackmailed, or coerced into doing terrible things by Voldemort threatening their families, but others claim this when they worked for him willingly.
 * The Memory Sorrowand Thorn series uses this trope once in the battle of the Stone of Farewell. The former mayor of some of the townfolk who follow Josua agrees to lead Duke Fengbald, leader of the enemy army, and his elite troops, to a weakly defended "back door" because his daughters are being held hostage. The trope is subverted when.
 * In the Lord Darcy story Too Many Magicians, was blackmailing  by claiming that Polish Intelligence was holding her uncle hostage.

Live Action TV

 * MacGyver, frequently. The first instance is in the episode "Deathlock".
 * This was used several times as a plot device in Hogan's Heroes, requiring the Heroes to rescue the daughter/father/what have you of the blackmailed individual.
 * 24, a lot.
 * Subverted in NCIS. is revealed to be the traitor because  was in trouble. Redemption Equals Death in this case, but it's unlikely that the traitor would have faced anything less than a long stay in federal prison.
 * In the Doctor Who new-series-three finale, Martha actually relies on a woman whose son has been imprisoned to betray her as part of a Batman Gambit. After the events of the entire year have been reversed, she goes and finds that woman (who has now never met her), gives her a flower and tells her there are no hard feelings. (In the DVD Commentary the cast argue over how much sympathy the character should get.)

Video Games

 * Olga Gurlukovitch turns out to be working for the Patriots because they kidnapped her newborn daughter, Sunny. This serves as a Kick the Dog moment for The Omniscient Council of Vagueness. Especially with The Reveal that . Who needs a "I have faith in you" motivational speech when you got "Screw up and an innocent child will die with you"?
 * In Tales of the Abyss it is revealed that
 * For once, Dr. Wily did it to a Commie. Dr. Cossack in Mega Man 4.
 * In Soviet Monsteropolis, YOU make commies do it!

Western Animation

 * Teen Titans: Robin is for a while forced to do anything the Big Bad Slade says, else he'll activate the lethal nanobots in the rest of the Titans.
 * In Exo Squad, spouse and son being held in a Neosapien stalag on Venus justifies the betrayal of La Résistance. A Heel Face Turn comes when  learns that Neosapien prisoners "sent to Venus" are killed on route.
 * Parodied in the Indiana Jones episode of Phineas and Ferb when . This being Phineas and Ferb,.