Poul Anderson

In the year 2047, the pioneering research vessel Event Horizon vanished without a trace. A signal has been detected, and a crew from the United States Aerospace Command hurtles toward the signal's source, in an attempt to find the state-of-the-art spacecraft. What they find is state-of-the-art interstellar terror. They must salvage their own lives or they will become ensnared in a new dimension of unimaginable fear.

"Once, military actions were entirely two dimensional, confined to the surface of land and sea, but then submarines and aircraft added a third dimension, vastly extended by spaceflight. Now, consider that if time travel is possible, the fourth dimension of time opens up new possibilities for combat -- necessitating new defenses, new strategies and tactics. A battle that was once decisively won might be refought, or a narrow victory might be subtly...