While playing baseball with Will, Penny and the Robot, Dr. Smith is injured. When he regains consciousness, he sees an alien dressed in a wizard’s costume. The others cannot see anything, and believe that it is merely the result of a concussion. The wizard continues to appear to Smith, tormenting him repeatedly.
When the Robot picks up signs of an alien life form, he leads Will and Dr. Smith to a cave where they encounter Zalto—the wizard Smith has been seeing. Will is impressed by the magician’s sleight-of-hand, but Smith continues to fear him. When he realizes that Zalto has a ship, however, he asks Zalto to make him his apprentice. When Zalto sees how easily he can manipulate Smith, he agrees.
Although Zalto does give Dr. Smith some training in magic, his main goal is to prepare him to carry out a publicity stunt that will help return Zalto to his former glory in show business. This comprises flying Zalto’s spaceship out into space and launching rockets that will explode and spell out the wizard’s name for all to see on many planets. Both Zalto and Smith are being deceitful. Smith plans to take the ship directly to Earth without carrying out the publicity stunt; Zalto, for his part, does not reveal that releasing the rockets will destroy the spaceship.
Although Smith offers to take the rest of his party with him, they refuse to have any part of his dishonesty. Will runs after Smith with his forgotten journal and ends up trapped with Smith in Zalto’s spacecraft and launched into space. The Robot returns with John, Maureen, and Don who demand that Zalto return their son and Dr. Smith, but he says that he cannot do it. Now aware of the ship’s fate, they attempt to establish communication, but cannot get through.
With Zalto’s craft approaching Earth, Will contacts Alpha Control, but when Smith launches the rockets, the authorities take it as a hostile act and launch missiles at the ship. Having failed to detonate Zalto’s rockets (and destroying themselves in the process), the pair are able to return to their planet. Meanwhile, Zalto is able to escape—managing to perform a disappearing act successfully for the first time in his career.
- When it was discovered that the episode's script was five minutes short, director Don Richardson asked Jonathan Harris and Al Lewis to ad-lib. Harris recalled, "Al and I resurrected an old burlesque bit, the up the ladder, down the ladder bit. You first Alphonse, no, you first Gaston."
- When June Lockhart, Mark Goddard, and Guy Williams are at Zalto's radio transceiver near the end of Act Four, Lockhart's line is "I do hope it isn't too cold [on Earth], Will wasn't too warmly dressed." And Guy Williams does a take that makes it look like he couldn't believe that was her line.
- Why would Doctor Smith think firing rockets at Earth would give Alpha Control the impression he and Will were friendly?
- On several occasions, Zalto calls Smith ‘professor’ rather then ‘doctor.’
- Why would the Robot need a tissue?
- Why is it that every time we see Doctor Smith’s suitcase, it is completely different? Considering he was a ‘reluctant stowaway,’ why does Smith have a suitcase at all?
- At one point, John asks, 'How’s Doctor Smith?' Maureen reples, ' Not very well. I just left him.' Don then asks her, 'Is he still seeing things?' Maureen then replies, 'Not anymore. He has his eyes shut.'