Dawn by Octavia E. Butler

When Lilith lyapo wakes from a centuries-long sleep, she finds herself aboard the vast spaceship of the Oankali. She discovers that the Oankali—a seemingly benevolent alien race—intervened in the fate of the humanity hundreds of years ago, saving everyone who survived a nuclear war from a dying, ruined Earth and then putting them into a deep sleep. After learning all they could about Earth and its beings, the Oankali healed the planet, cured cancer, increased human strength, and they now want Lilith to lead her people back to Earth—but salvation comes at a price.