The Robinsons hurriedly lift off in the Jupiter 2 after having become aware a huge comet is hurtling towards the planet. Once in space they find themselves pulled magnetically into the interior of another spaceship.
Don and John board the vessel. They discover they are now inside a fully automated prison colony. The warden is a computer and all the prisoners aboard have been frozen. When they don’t return, Smith, Will and the robot go in search of them.
Don is mistaken for a prisoner by a robot guard and frozen. Dr Smith accidentally unfreezes a prisoner known as Mr Phanzig who in turn unfreezes other prisoners. Together they stage a mass break-out.
Meanwhile John discovers that the clock that measures the time of each alien felon’s sentence stopped working two hundred years ago. John repairs the clock and the computer announces the men have all served their sentences and are now free.
The role of lead prisoner Mr Phanzig was played by German-born character actor Marcel Hillaire (1908 -1988). For a time he was a real-life prisoner in Nazi Germany when it was revealed he came from Jewish heritage.
He went on to have a successful career in American films and television including featuring as a film director in Woody Allen’s second movie TAKE THE MONEY AND RUN (1969).