Land of the Giants

The Earthlings witness one man drop an envelope as he is shot by the police, and another elderly man try and find it. Then they receive a radio message from another Earth craft. Steve suspects a trap and plays it cautious, but Valerie and Fitzhugh go and get captured along with Steve by the elderly man, Professor Gorak. Gorak is in charge of an underground resistance, and the envelope has the coded names of the members.

Holding Fitzhugh and Valerie hostage, Gorak forces the others to try and break into the impregnable vault. The vent is blocked by debris, so Steve comes up with a plan to smuggle Fitzhugh in so he can open the box holding the letter and then destroy it. That plan goes awry as well when Fitzhugh is knocked unconscious. Using Fitzhugh's walkie-talkie, Dan and Steve distract the guards and get into the vault, but almost get captured. Gorak breaks in and shoots the guards while being shot and killed himself. The Earthlings destroy the letter and escape.