In Their Absence

In After Doomsday by Poul Anderson, an interstellar spaceship with a human crew and one alien passenger returns to the Solar System to find that Earth has been sterilized by as yet unknown aliens.

In The Avatar by Anderson, an interstellar spaceship with a human crew and one alien passenger returns to the colonized Phoebean System and from there is escorted through the T machine gate to the Solar System there to be held incommunicado by order of the anti-stellar clique within the World Union government. (Ships with only interplanetary capacity traverse interstellar and vaster spatiotemporal distances by orbiting around T machines.)

In both cases, heavy things have gone down in the explorers' absence but the enemy is alien in the first case and human in the second. Meanwhile, stuff going down on Earth keeps me away from this lap top.