The Siege of Eternity — Frederik Pohl

The aliens aren't coming. They're here.

We've captured several of them,. Are they our saviors, or are they out to destroy us? We've seen no spaceships, received no ultimatums--but the aliens may have a more insidious plot....

Government agent Dan Dannerman and astronomer Patrice Adcock were kidnapped by the aliens and have been returned in altered states, cloned and implanted with strange devices. To what end?

Before the reasons behind their abduction can be made clear, a wave of extremist threats and terrorist attacks sweeps the globe. Are the attacks a reaction to the aliens' arrival or a part of their plan? A race around the earth and into space begins, as humankind desperately tries to prevent the aliens from establishing a beachhead on Earth.

The siege has begun.