A sleeper cell is a person who remains a dormant member of a group while belonging to another group for undisclosed reasons. Usually the sleeper cell status is kept a secret. A sleeper cell is a clandestine group of terrorists who work underground and come back to life suddenly to achieve the target set by their superiors. 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. Sleeper agents who have been discovered have often been natives of the target country who moved elsewhere in early life and were co-opted (perhaps for ideological or ethnic reasons) before returning to the target country. This is valuable to the sponsor as the sleeper's language and other skills can be those of a 'native' and thus less likely to trigger suspicion. One of the most insidious tactics at a terrorist organization's disposal is the implementation of a sleeper cell. This consists of secret agents who receive specialized training in their home countries and are then assigned to assimilate into another country's culture and society. These agents may spend years performing their regular duties while living deep undercover, then suddenly receive orders from their overseas handlers to either commit an act of terrorism or provide aid to those who will.