Exile (Five Worlds)

In the year 2500 A.D., four of the nine planets in our solar system have been colonized, and a fifth, Venus, is being terraformed. Then a bloody coup on Mars puts a ruthless leader in charge, and suddenly the Four Worlds are ripe for invasion, with the fate of all humankind hanging in the balance. And there are others, not human at all, who watch the battle, and plan.