The End of Eternity is a 1955 science fiction novel by American writer Isaac Asimov with mystery and thriller elements on the subjects of time travel and social engineering. Its premise is that of a causal loop – a type of temporal paradox in which events and their causes form a loop. In The End of Eternity, members of the time-changing organization Eternity seek to ensure that the conditions which led to the founding of Eternity occur as history says they occurred. The protagonist, Andrew Harlan, is placed in a situation where he must decide whether to allow the "circle" to close and Eternity...