After a close call when their water storage tank almost crushes Don, the Robinsons realize they are facing a severe water shortage during a hot, dry season on the planet. Smith soon makes matters worse by having a shower, leaving the party with only 24 hours of water.
With no other recourse, the entire party sets out with buckets to try to find a source of fresh water, but Smith, irked by Will's repeated references to his age, soon returns to the Jupiter 2. The Robinsons soon find a pool of water, but it is undrinkable. Despite that, there are numerous melon-like fruit growing round it and they take a bunch back to camp for testing before eating any; unbeknownst to the Robinsons, though, Debbie the bloop tries one.
Later that day, after they have returned to the ship, Maureen is horrified to see Dr. Smith eating the still untested fruit. Not knowing whether or not the fruit is poisonous terrifies Dr. Smith. In his terror he is certain that the fruit was left out deliberately so that the Robinsons could be rid of him. He runs off into the wilderness alone.
Further problems mount at camp when one of the fuel cells in the water purifier turns out to be defective. The next morning, John, Don and Will go looking for Smith after he has spent the night alone away from camp. Will is genuinely worried, and chides Don for making light of the fact that Dr. Smith may already be dead. Meanwhile Maureen has been testing the fruit and it turns out to be unsafe for consumption, although not poisonous. As she is reporting to John on the radio, Penny looks out from the Jupiter 2 to see that Debbie has more than doubled in size over night, although they find her personality unchanged.
The men eventually find Dr. Smith, and are shocked to discover that he has grown to enormous size. Smith, however, remains unaware in the change in his stature, but reacts in shock when the others convince him. He begins recriminations and threatens to have his revenge on the Robinsons for what he still believes they deliberately did to him, but he is soon reduced to self-pity. Only when Maureen later arrives is he convinced to return to camp where he and the bloop must sleep outside the Jupiter 2. During the night a sudden rainstorm comes up and soaks the pair, restoring them to their normal size. The Robinsons cannot help but laugh when they see the wet and bedraggled Dr. Smith enter the ship, but in spite of his hurt feelings, at least their water shortage is over.
Although eating the fruit attempts to expain Smith's height, none are given for his uniform. Smith's entire uniform grows along with him....then shrinks back to normal when Smith shrinks back to normal. Actually, Smith should have burst through his clothing, tearing it to shreds when he began to enlarge.
- When Don and John face down the giant Smith, they wield unusual lasers that, for whatever reason, are never again used in the show. The Robinson's arsenal was often inconsistent at least for the first two series, with several variants of pistols seen throughout the first season. Another example is the slender laser pistol seen in The Raft.
- A consistent thread through the first half of the first season is the suggestion that the life forms on the planet have adapted to the wild climatic conditions by being able to grow rapidly although perhaps nondiscriminately. This would explain the giant in "There Were Giants in the Earth" and the cyclamen in "Attack of the Monster Plants." Smith's reaction could be explained if microorganisms in the fruit started this process in him.
- Again, Galileo's square cube law is ignored with respect to the gravitational forces that would pull on Smith. Perhaps the process also increased the relative strength of his bones. Also, as Smith shrinks something must have happened to the extra mass that comprised him as a giant.
- The Robinson's lack of water is not unusual given the heat due to the planet's erratic orbit, but it seems odd that no attempt is made to use the inland sea seen in "The Hungry Sea" and "There Were Giants in the Earth".
- An overhead panorama of the Jupiter II campsite is shown. The view looks as though the spaceship has been gently lowered down and carefully placed amidst an alien rocky outcrop, instead of the aftermath of an out of control, pancake crash landing (well sort of ) seen in “Island In The Sky” (ep3). This background of rocks doesn’t appear to match any of the close up scenes viewed around the spaceship either.
- Though Don’s foot is nearly crushed after an encounter with a giant boulder, he shows no sign of limp or obvious discomfort on the long trek to search for water.
- We are treated to a great shot of Maureen ascending the glide tube from the inside, showing her rising from the lower level to the upper deck.
- After Dr Smith returns to normal size, the Robinsons and Don are standing in the Jupiter II facing the airlock area with the freezing tubes behind them. Smith enters the elevator and descends, but the Robinsons are still facing the view-port, instead of turning around to look at him as he enters the elevator.
- Debbie the Bloop has its own doll???
- When they discover the Bloop’s increase in size due to eating the fruit, Maureen doesn’t think it’s important to covey this to John, as “he already has enough to worry about”.
- Yay! Here comes the rain. Let’s all give thanks and celebrate, but never mind the lightning bolts! Meanwhile, the resultant precipitation magically shrinks Dr Smith and the Bloop back to normal. How? Who cares, hooray!
- Dr Smith to John - "I'm sure you'll find it, (the water source), I'll be rooting for you. [Smith then gets up to go to his cabin]. John: "Where are you going?" Smith: "To my cabin to start rooting"
- [John and Don discover Dr. Smith taking a shower with the last of their water supply] John: “I ought to kick you clear into orbit for taking a shower at a time like this.” Dr Smith:” I couldn't wait another day. I was losing precious body fluids besides feeling very icky”
- Dr Smith: “I know how you all feel about me! Another mouth to feed! Another thirst to quench! "Oh, yes, let's get rid of him! This is our chance." That's the way your evil minds worked, wasn't it?”
- Will: “Gosh, it's not so bad being big. Think of all the marvellous things you'll be able to do. Like, gosh, you'll be able to get bird's eggs without even climbing.“
- Will: [excited that the water conversion unit is working again] We should get a pint of water apiece from it every day. Dr Smith: [un - enthused] A pint. I'll use it for eyewash - for one eye!"