It was written by Malcolm Marmorstein and is based on characters created by Alexander Key, who also wrote the novelization of the film for Disney.

Ike Eisenmann, Kim Richards, and Denver Pyle reprise their roles as Tony, Tia, and Uncle Bené—humanoid extraterrestrials with special powers including telepathy and telekinesis.

Uncle Bené drops them off in their flying saucer at the Rose Bowl Stadium in Los Angeles, California, after which the siblings quickly become separated from each other.

Under its influence, Tony is completely hypnotized and does everything his kidnappers want him to do, including stealing gold from a museum exhibit and stopping Tia from finding them.

With Tony at his robotic bidding, Dr. Gannon hopes to achieve recognition within the scientific community and worldwide power, while Letha merely wants a return on her investment.

The gang follows the goat back to the hideout and they free Tia as Tony, Letha, Sickle, and Victor drive to a plant to steal plutonium.

The people working at the plant make arrangements for the money as soon as possible, but Tia reaches the site in time, where she and Tony battle to turn on the cooling system.

[citation needed] Jack Soo (Mr. "Yo-Yo" Yokomoto) was diagnosed with esophageal cancer in the autumn of 1978, several months after the film's release.

[1] The otherwise vacant lot upon which the children's dilapidated mansion hideout stands was at the Alameda Street railroad yard in California, where the Rochester House (a relic from the 1880s)[2] was waiting for restoration and relocation.

[citation needed] Scenes of Dr. Victor Gannon's mansion, the location of his laboratory, were filmed at Moby Castle on Durand Drive, Hollywood Hills, Los Angeles.

[citation needed] The gold bar robbery sequence was filmed at the Natural History Museum in Exposition Park, Los Angeles.