Cronos

From the man who has won more Hugo and Nebula Awards than any other author in the history of fantastic literature, three complete novels that embody the concept of time travel. LETTERS FROM ATLANTIS Time travel has allowed Roy's consciousness to enter the mind of the heir to Atlantis's throne. But if he was in an Atlantis unlike anything the researchers had predicted, then what were its secrets? And when would it be destroyed? PROJECT PENDULUM The nature of time mechanics requires that the two travellers' masses be precisely matched; for that reason, the first time travellers must be a pair of identical twins. What neither planned on, however, was how the inhabitants of those times would react to their presence.... THE TIME HOPPERS In the 25th century, the only escape from suffocation in a totally controlled environment is to 'hop' backward through time. However, since time-hopping is outlawed, it must be stopped - but not too quickly. For the history of the 1970s includes the arrival of hoppers who have not yet left the 2490s!