Ducking a SID man, the Earthlings are spotted by two children on a picnic. Giving chase, the children fall down an abandoned well. Steve and Dan are captured, while Valerie and Betty contact the children's mother and suggest she have Steve and Dan help with the rescue in return for their freedom.
Inspector Kobick rejects the idea, but Steve and Dan volunteer their services without condition. They are lowered into the well, which is closed off to giant-sized access due to cave-ins. Meanwhile, Mark and Fitzhugh get hold of the sewer plans and find an old drain pipe that leads into the well.
While Steve and Dan verify the children are alive and get oxygen to them, Mark and Fitzhugh get to them. Coming up with a plan to escape, they manage to dig into a parallel pipe and plan to climb back up the oxygen mask tube while the children get out. Another cave-in puts the kibosh on that plan. When the four men try to make a break for it through the drain pipe, the grateful parents distract Kobick long enough for them to escape.