In TimeMaster, wormholes are found in space. They are, as every good physicist knows they must be, stabilized by nearby negative matter. But this negative matter just happens to be in the form of intelligent life. An extremely wealthy individual uses these wormholes to travel faster than light, but he draws the line at monkeying with time. But when his family is threatened by terrorists, he uses time travel in self-defense. Forward postulates, as Heinlein does, that there's only one unalterable timestream, and anything that you go back and do is something that historically already happened at that time and place. No paradoxes allowed. But you can certainly send messages back saying "there's a bomb in box 456 on flight 123," being careful not to say whether it was found or whether it detonated..
(By Keith Lynch, The WSFA Journal October 2002)