they want. Jan invites Harkness to stay at their house. A grouchy Groves complains about Harkness being there at breakfast, but Ruth insists that he remain. Oakes arrives, and he and Harkness head out to look for the sabretooth. They find it and kill it, but Harkness says he fears there are others. Back at the lab, Ruth and Groves quarrel about their deteriorating relationship. He throws her out, then injects himself with the serum he has been using to turn cats into sabretooth tigers. He reverts to the Neanderthal Man. Out in the woods, he kills hunter Jim Newcomb and his dog, then returns home and becomes Groves again. He writes in his diary that this most recent regression was the fastest yet, and the recovery was the slowest. "I gloried in my strength and ferocity", he writes, also noting that he was overcome by the "hungry urge to kill." Then he spontaneously turns into the Neanderthal Man and runs off. Harkness sneaks into Groves's lab and finds photos that Groves took as he experimentally regressed Celia, his deaf-mute maid. Buck Hastings and Nola go on a picnic, and he snaps some glamour shots of her. But the Neanderthal Man kills him while Nola is behind a bush changing clothes. As she looks at Buck, dead on the ground, the Neanderthal Man carries her off, kicking and screaming. Oakes phones Jan and says Buck has been murdered. During the call, Celia sees Nola outside. Harkness carries Nola in. She is hysterical and her clothes are torn. Buck, she says, was killed by something "not human." Then she cries, "He tried to pull me by my hair and then he ... then he ..." and collapses into tears, wailing. Jan calls Webb's, tells Webb what happened and asks him to send for the local MD, Dr. Fairchild. Harkness shows Jan and Celia the photos of Celia being regressed to a Neanderthal Woman. Celia signs that she has no memory of it. Harkness then notices that one of the lab cats starts to yowl whenever it sees a syringe. When he injects it, it turns into a sabretooth and escapes. Jan and Harkness read Groves' diary. He wrote that the serum works on cats, not dogs, and not fully on women but on men. They set out to find the Neanderthal Man before the State Police and Sheriff's posse can. They