While John, Will, Smith and the Robot conduct tests on particles, a cosmic storm hits their tiny planet. Much to their shock, their experiment accidently imprisons a very angry man by the name of Chronos. Chronos demands to be released, and Will obeys. Sadly, moments later, Dr. Smith’s poor people skills manage to infuriate Chronos even further.
When it becomes obvious that Chronos has the ability to manipulate time, Smith starts to get an idea. Chronos decides to take Will away with him to work in his time factory, and though the boy refuses, Chronos hypnotizes him and takes him away anyhow. Dr. Smith informs John, and John and the Robot go after Chronos and the kidnaped Will. Though John clearly orders Smith to go back to the spaceship, Smith becomes frightened at being by himself and follows after them instead.
John quickly finds Chronos and insists that Will be set free. Chronos refuses, declaring that the Robinsons have caused him to “lose time” and that he now intends to make it up by any means possible. Smith tries to bargain with Chronos for youth and passage back to Earth. He requests that Chronos send him back to the day when the Jupiter 2 first took off, and when the Time Merchant’s back is turned, he sneaks off without paying.
Chronos is furious and demands that John settle Smith’s account by handing over part of his own life span. Chronos also warns that Smith may alter the course of history by doing things differently in the past. They observe the Doctor’s actions through one of Chronos’ many machines, and discover that Smith intends not to board the Jupiter 2 so that he will never be lost in space with the Robinson family.
Although it seems that this would be a very good thing, it turns out that without the added weight of Dr. Smith aboard ship, the Jupiter 2 will collide with an uncharted asteroid and be destroyed.
When he learns this, John realizes that it is necessary for Smith to board the Jupiter 2 before history is altered and the whole Robinson family ceases to exist. John tries to persuade Chronos to return Smith, but the Time Merchant will not do so, saying that the power such an action would require would destroy his machine. John then asks if the Robot might be allowed to go after Smith instead. Again, the Time Merchant refuses, saying that he won’t allow any more time traveling until he is given compensation. Having little choice, John agrees to pay Chronos some of the years of his life. A bargain is made, and the Robot travels back in time to convince Smith to board the Jupiter 2. The plan goes awry quickly when the Robot’s tapes are erased on arrival and he no longer remembers why he is there or any of his life with the Robinson family at all.
Will begs to be sent through time as well so he can fix the Robot, and Chronos reluctantly agrees, but will only allow the boy two minutes to complete the task. Will makes the journey and tries to remind the Robot of his mission, but time runs out before he can be certain of his success. Will is transported back to his father and Chronos, and Robot is left alone and very confused.
Luckily, after a brief conversation with Dr. Smith, the Robot remembers his orders and tries to coerce Smith into boarding the Jupiter 2. Even when the Robot tells Smith that the Jupiter 2 will be destroyed without his help, Smith refuses to go along. Robot leaves to get onto the ship by himself, and once he is alone, Smith has a change of heart and follows. The pair makes it to the Jupiter 2 just in the nick of time to get on board.
Having observed all of this, John forces Chronos to transport Smith and the Robot back to the present. The time machine is then destroyed by a power overload, and Chronos may very well have been killed in the explosion. Will, John, Smith and the Robot return to their own dimension, and everything is back to normal.
- Mark Goddard, Angela Cartwrightand Marta Kristen are credited but do not appear in this episode.
- Guy Williams' stunt double can be seen in the fight scenes in the Time Merchant's lair.
- Jonathan Harris' stunt double can be seen when Dr. Smith is returning to the Time Merchant's lair.
- Dr. Smith and the Robot are able to sneak about the ship without being seen despite that area being monitored on video as seen in the pilot.
- The Robot's shipping crate is labelled "General Utility Non-Theorizing Environmental ROBOT".
- Smith's confession to the Robot about why he cannot go with him to board the ship seems sincere, made so by Jonathan Harris' excellent acting.
- Dr. Smith's room back at Alpha Control has a wall-mounted rotary dial telephone.
- The Salvador Dali influence is clearly seen on Dr. Chronos' planet that has pocket watches and clockfaces folded on tree branches as in the painting The Persistence of Memory.
- The exterior of the Jupiter 2 was made from masonite, a type of hardboard made of steam-cooked and pressure-molded wood fibers. Its distinctive speckled surface can be seen in this close-up of Smith's hand on the exterior hatch control. The fitting where the tether for the space walks is attached can be seen directly above Smith's hand.
- When Chronos was trapped as a result of their experiments, why didn’t Will immediately call to his father for help? John was just outside, and it wouldn’t have taken any time at all to fetch him. Why wait so long to do the sensible thing?
- Why was Smith so upset about not getting to be immortal? Will had just been kidnaped! Shouldn’t that have been a greater concern?
- Why did Smith’s clothing change when he traveled into the past?
- Why did all the military personnel call Smith “Doctor Smith?” Wasn’t he supposed to be “Colonel Smith” back then?
- The Robot was crying again. Apparently, they were real tears that he had to wipe away. Why would anyone design a robot with tear ducts in its bubble?
- Smith claims to be 27 years old. *snicker* Suuuure you are, Doctor Smith!
- Where are Penny, Judy and Maureen throughout this episode?