Inspector Kobick, an officer with the police's Special Investigations Department (SID), develops a way to track the humans using a scanner which detects a metal unique to Earth. Steve has everyone get rid of all articles containing the metal, but Dan has a surgical pin in his leg made of the unique material. After Dan is to live on his own in the marshes, Steve gets the idea; evade capture by having the pin surgically removed, so he seeks out Dr Brulle—the giant surgeon who saved Barry's life previously—but the doctor is in prison, and the only chance to reach him lies in contacting his nurse, whose real loyalty may be to Kobick.
Guest Stars: Paul Fix (Dr. Brule), Robert Emhardt (Mr. Secretary), Bill Fletcher (Sgt. Karf), Kevin Hagen (Insp. Dobbs Kobick), Sheila Allen (Nurse Helg), Gene Dynarski (Warden Barmak)