Parallel worlds, both with scientific laboratories in caves miles underground.  One world is inhabited by Homo sapiens, the other by Homo neanderthalensis.  Ponter and Adikar were using their Quantum Computer to connect to other worlds, when Ponter disappeared.  In the other world, a man (Ponter)  is found in a tank of heavy water, how could he have gotten there and where did he come from?  Security was tight and the tank was sealed.   Homo sapien, Professor Mary Vaughan, runs DNA testing and finds that the man is indeed Neanderthal, but how he got there they haven’t a clue.  With the help of Ponter’s implanted computer, they are able to communicate, but Ponter has lost all hope of returning to his family and friends.

While back on the Homo neanderthalensis world, Adikar is being accused of murder.  A man has disappeared and there is no evidence of where he is.  While Adikar has an idea about his disappearance, he is not allowed back into his laboratory.   Adikar gets Ponter’s daughter to help him in his trial, but it isn’t enough.  So Lute, his woman mate, causes trouble in the viewing room, so that Adikar can get to the laboratory to try and get Ponter back.  Hominids by Robert J. Sawyer is the first book of a trilogy.  Humans is book two and Hybrids is book three.