One day a flying saucer lands in Moominmamma's vegetable garden. It is apparently unmanned and she and Moomin salvage a strange box-like apparatus which looks rather home-made, but which has many remarkable properties. The Inspector is on the war-path trying to nab extra-terrestrials and when the Moomins find one, a runaway child, they have to hide him, quickly deciding that he has probably not come to invade Moominvalley. Their task isn't made any easier by the fact that the box-like apparatus has now made the Inspector iridescent, this fascinating the child so that he follows the Inspector everywhere.
