First Season Episodes - The Space Trader (episode 23)

An alien Space Trader tries to trick the Robinsons into trading him a human -namely Smith.

John Robinson saves Dr. Smith from a water tank that hurtles toward him during a cosmic storm. Some distance away, the Space Trader turns off his storm machine and gloats over the successful first step in a plot to get the Robinsons to trade with him. Damage at the campsite is extensive and the Robinsons are forced to ration themselves until the hydroponic garden can be recultivated. 

Will and Smith wander into the Space Trader's spaceship-store, well-guarded by two chained monsters. The Space Trader shows them some of his exotic wares. But back at the campsite, John rebuffs the Trader's offers. The Trader makes a deal with Smith to supply the gluttonous doctor with 12 days of food in exchange for the Robot. That night, Smith lures the Robot to the Trader's store and receives his first parcel of food. 

Will, meanwhile, has found the Robot at the Trader's store and returns to the Jupiter 2 with the news of Smith's deal. Ostracized, Smith seeks reinstatement with the Robinsons by bargaining with the Trader for return of the Robot. The Trader proposes an alternate trade -Smith! Smith agrees and lends his hand print to a strange contract which the Trader says he will not collect for 200 years. 

After several days, however, the Trader shows up to say that he will be back later to collect Smith. The Trader holds up the contract, and as it glows, Smith walks helplessly away with the man. Will goes after him, and after diverting the dog- monsters at the store, he and Smith make a run for the Jupiter 2. Suddenly, the Robot destroys the contract, freeing Smith. The dog-monsters then turn on the Trader, telling him he has failed, and chase him away. 

Later, while hunting truffles, Smith dons a mysterious crown, which possesses the doctor.

Filming