Man wakes to discover he's been kidnapped and is part of a (non-human) alien project to prevent human extinction. Soon enough he finds he's been given some real power, but also some big responsibilities. With a freshly-young body, he feels better and will live longer, but it also has the side benefit of helping lots of young women into his bed, and then out, empowered, to change the world. There's fun to be had, but meanwhile, the world is changing.