Kid Flash and Mal escape the alternate Earth of Jupiterius and return to the prehistoric past, this time preventing the death of the caveman whose demise had warped history. However, they accidentally bring the caveman back to modern times with them. Mr. Jupiter gives the Titans the task of training Gnarrk, as the Cro-Magnon is christened, to become a civilized present-day man. Robin returns to the ranks to help out, only to find that Gnarrk’s education has taken on an added importance: the caveman has witnessed a payoff between underworld figures and a respected city councilman, and must be trained quickly to become a believable witness in court. When gangsters attempt to assassinate Gnarrk, Lilith, with whom he is slowly falling in love, takes him to a supposed place of safety, but the hoods find them and attack. Lilith is wounded, and Gnarrk goes berserk, easily overcoming the hired killers. Robin and the Titans intervene in time to stop him from committing murder, and Gnarrk agrees to abide by present-day law and refrain from killing in revenge. Lilith recovers, and Gnarrk’s testimony results in the conviction of the crooked councilman.