Ponter Boddit, a physicist in a world in which Neanderthals are the dominant primates, is performing a quantum computing experiment in a Canadian mine, where cosmic rays won't disturb the test's delicate parameters. Suddenly, he is transferred into a heavy water tank in the same mine, but in the universe in which humans predominate. Human scientists are alarmed, then amazed by the spluttering Neanderthal in modern clothing with a curious AI implant in his wrist. Ponter's scientific partner, Adikor, is equally shocked, but what's more, he now faces an inquiry into his best friend's disappearance and suspected murder. Ponter is a most winning creation--thoughtful, brave, and charming as, facing the loss of everything he loves, he befriends a wounded female scientist in the strange human world.