The Walsh family welcome a mysterious stranger into their home. Impressed by the man's advanced intelligence and linguistic skills, Mr Walsh offers him a teaching job.
Curious about Adam's weekend bushwalks, Bernie, Jean and Peter follow him to the Blue Mountains where locals have reported strange lights in the sky.
Aboard the spacecraft, Bernie, Jean and Peter learn the truth about Adam and Varossa's people, the Soshunites. Meanwhile back on Earth, the teenagers are reported missing.
On their return to Earth, Adam and Varossa are arrested. Bernie, Jean and Peter have a hard time convincing the authorities that their friends are from another planet and need help.
Professor Mayer meets the peaceful Soshun while authorities on Earth prepare for an invasion.
Professor Mayer takes the plight of the Soshunites to the United Nations.