At the end of this century Ross Murdock is given the choice between prison and a dangerous role in a secret mission. Accepting the latter, but determined to escape at the first opportunity, the intelligent young man finds himself involved in a project which demands that he be projected back to various periods in history. For the Americans, aware that the Russians, somewhere in time, have learned the secret of space travel, must for the sake of national safety, obtain the same secret. Hurled back into the earliest ages of man, Ross' volatile intelligence is, for the first time, stimulated as he risks death, posing as a member of prehistoric worlds. By the time the Americans gain control of the secret, Ross is rehabilitated and is a willing participant in the benevolent army of the future. An interesting idea, well handled by Andre Norton, science fiction expert, who projects his reader deftly both backwards and forwards in time and injects his narrative with considerable and interesting historical information.