The siege of eternity

The Siege of Eternity is a 1997 science fiction novel by American writer Frederik Pohl. It is the second novel in The Eschaton Sequence (it is the sequel to The Other End of Time, which was published in 1996). The Eschaton Sequence is about the adventures of Dan Dannerman, an American government agent of the near future who becomes involved with the discovery of advanced and warring aliens. In The Other End of Time, Dannerman is part of a group that is abducted by space aliens. In The Siege of Eternity, Dannerman and his cohort escape, only to find that they have been cloned and experimented on. Moreover, the aliens are battling for control of the powerful "Eschaton" a future which gives everyone eternal life.