Earth's protector BGY-11, better known as the 'Big Guy', is decommissioned after boy robot 'Rusty' is successfully deployed; but when a new threat proves to be too much for Rusty alone, the Big Guy returns to join the fight.
A scientist attempting to develop telepathy instead develops a taste for human brains after an accident in his lab. Meanwhile, Dr. Slate stumbles across confidential files detailing Lt. Hunter's role as the Big Guy's "chief mechanic".
Dr. Slate, the Big Guy and Rusty access Dr. Gilder's memory in an attempt to locate the Legion ex Machina. But are they too late to stop the Legion's most lethal plan yet?