Young Tom Fortnam is thrilled when he receives his guaranteed to grow mushroom seeds by special delivery mail. His father Bill is then approached by a friend, Roger, who thinks people are disappearing. Bill isn't quite sure what to make of it all until Roger's wife calls him to say that Roger has vanished, as has all of his clothes. When he visits Roger's house, he sees that Roger's son, who is the same age as Tom, is also busy growing mushrooms in the basement. Convinced there is a connection, Bill confronts his son - with fantastic results.