double agent

double agent
    n 1: a spy who works for two mutually antagonistic countries
    

45 Moby Thesaurus words for "double agent":
      Benedict Arnold, Brutus, CIA man, Judas, Judas Iscariot, Quisling,
      archtraitor, betrayer, cloak-and-dagger operative, cockatrice,
      conniver, conspirator, conspirer, counterintelligence agent,
      counterspy, double-crosser, double-dealer, espionage agent,
      informer, inside man, intelligence agent, intrigant, intriguer,
      machinator, military-intelligence man, naval-intelligence man,
      operative, plotter, quisling, rat, reconnoiterer, schemer, scout,
      secret agent, serpent, snake, spotter, spy, spy-catcher,
      timeserver, traitor, treasonist, trimmer, turncoat,
      undercover man