All of this brainwashing makes this young man the perfect sleeper agent.
所有这些洗脑使这个年轻人成为完美的卧底特工。
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In this case, the sleeper agent is activated or made to go into action when he's shown this playing card, this Queen of Diamonds, and given instructions about the next person he's supposed to kill.
A sleeper agent is a spy who is placed in a target country or organization, not to undertake an immediate mission, but rather to act as a potential asset if activated. Sleeper agents are popular plot devices in fiction, in particular espionage fiction and science fiction.