Will, Penny, Dr. Smith and the Robot work to put together a time capsule that they bury during the night. On their way back to the Jupiter 2, they encounter a werewolf. The Robot blasts it and it leaves. They all run back to the spaceship and tell Don and John and Maureen what they saw, but no one believes them. John says if Smith wants to prove that there is really a werewolf, he should catch it. Smith is frightened, but Will thinks it is a good idea.
The next day, Will and Dr. Smith go to catch the beast. They notice that someone has dug up their time capsule, and notice large wolf prints nearby. They follow the tracks and are led to a spaceship owned by a family of hillbillies. The hillbilly clan consists of a mother and her grown daughter and son. The son, Keel, is very strong and very stupid and does not speak. The daughter, Effra is quite a spitfire who informs Will that her family will only be there temporarily. They plan on staying just long enough to plant and harvest their crop, and then they will leave. Dr. Smith immediately tries to obtain passage to Earth, but the mother, Sybilla draws her shotgun and angrily tells them to leave.
Smith and Will go back to the Jupiter 2 and tell the others what they have seen. Later, Effra comes to the Jupiter 2 to borrow some stew seasoning. She flirts with Don and Judy becomes jealous and possessive. That night the Robinsons are awoken by loud chanting. They follow the noise to the croppers' ship and see the hillbilly family dancing and chanting in a field of frightful plants. The croppers refuse to answer any questions and demand that the Robinsons get off their property at once. Dr. Smith attempts to flirt with Sybilla and asks if he can come and visit her the next day.
Dr. Smith does return the next day with a basket of presents and Will in tow. Will and Smith both notice that the strange plants have grown significantly since the previous night and that the hillbillies seem to have become rich. Smith tries to woo Sybilla, and after a while, she starts to like it. Meanwhile, Effra decides that she wants Don and goes to the Jupiter 2 to seduce him. Don refuses her, and she is infuriated, declaring that he has made a deadly mistake, and she will cast a spell on him.That night, Doctor Smith announces that he has asked Sybilla to marry him. He also says the croppers are leaving in the morning, and that he intends to go with them. John warns Smith that it is a bad idea to leave with a woman he knows so little about, but Smith will not listen. No one is happy for Smith and they suspect that he does not really love Sybilla—he is just using her to get passage to Earth. Smith dismisses their warnings and opinions, packs a suitcase, and leaves for the hillbilly ship. Later that night, Will decides to make a last attempt to convince Smith to come home. When he arrives at the croppers' land, he is shocked to see the plants have grown enormous. The werewolf appears and startles him and he is nearly devoured by one of the plants. Effra pulls Will free, and much to his surprise, she reveals that the werewolf is actually her brother, Keel. Will tries to warn Smith about what he has discovered, but Smith does not pay any attention.
Will runs back to the Jupiter 2 to tell his family about the croppers and their killer plants. Don and John grab their gas guns and start to kill the plants as they approach the spaceship. At the hillbilly ship, the croppers make their final preparations to leave. Smith is saddened to discover that they do not plan on going by Earth at all. He then discovers his new daughter is a witch, and his new son is a werewolf. When he finds out the plants eat everything, including humans, Smith runs back to the Jupiter 2. The space croppers’ ship blasts off as Don and John destroy the last of the plants. The Robinsons are safe from any further danger but Dr. Smith is very unhappy and bemoans his failed romance.
- When Sybilla opens the semi-cylindrical door of the greenhouse to examine her plants, the prop used for the greenhouse is the four man bathysphere used in the 'Voyage to the Bottom of the Sea (1964)' episode: "The Condemned.
- WHOOPS! Will heads directly to the croppers ship to warn Dr. Smith, but doesn't know Dr. Smith is inside the Jupiter 2 packing. When Maureen comes upon Dr. Smith while looking for Will, Smith then announces his forthcoming marriage to Sybila then leaves. When Will gets to the croppers ship, Smith is there well ahead of him and sweet-talking Sybila, never having passed Will on the way there.
- When the werewolf reverts back into Keel, its footprints revert from wolf tracks to shoe tracks instead of to footprints from the bare feet they should be.
- This is one of the first episodes produced after the very popular Batman series premiered on ABC and is perhaps the first to borrow the camp stylings of that series in order to compete in the ratings.
- The killer plants have been used twice before, as the Cyclamen in "Attack of the Monster Plants" and "Welcome Stranger".
- In the preview for this episode, the Robot mispronounces canis lupis as hanis lupis when they are preparing the time capsule.
- What did the fact that Keel was a werewolf have to do with anything else in the episode?
- Where did Smith get the safari hat?
- When the hillbillies wake the Robinsons with their chanting and planting, it appears to be night-time. So why wasn’t Keel a werewolf?
- What exactly is the relationship between the hillbillies and the plants? Sybilla says that the plants “will provide,” but It's unclear what she meant by that. At the beginning of the episode the croppers are dressed in filthy rags and have no food. Later, they have plenty and are dressed in beautiful expensive gowns. Did the plants grow them dinner as well as fancy clothes and diamond earrings?
- Why do the hillbillies have a shotgun? Wouldn’t a shotgun be considered very much out of date for them?