A heat wave and drought leaves the Robinson party low on water, and they take a trek to the source of a river, find brackish water, but also alien fruit that they harvest and bring home. Unknown to them, Penny's pet, Debbie, eats some of the fruit. That night, while they are running tests on the fruit, Smith (who's been missing since he left their trek to the water source) eats some of the fruit. He's convinced the Robinsons were trying to kill him, and runs off into the wilderness. After recording a rant on tape, he buries the tape and carries on. The Robinsons find him... three times bigger than his normal size. Debbie is also enormous.