A giant has been framed for a murder he didn't commit and now awaits execution for the crime. Steve overhears the real murderers discussing their crime shortly after they have attacked him. He vows to find a way of freeing the innocent man and seeing that justice is done.

First Fitzhugh, Barry and Valerie, then Mark, Steve and Dan, are captured by Kronig, a giant industrialist who is a chess fanatic. He wants to demonstrate his superior mind against the Earthlings. To do so, he tells them to pick there best chess player to play with him. If they win, they will get there freedom.