Aliens plot to turn humans into water-breathers, then to force them into the ocean so that the surface world can be occupied.; The proprietors of the Mystery Museum are about to close it down due to bad business, but a man shows up who agrees to do demonstrations of real magic. However, he really only wants access to the magic cauldron on display, which will give him fantastic powers he can use for criminal purposes.; An ancient feud between two Scottish clans re-emerges in the present, with the head of each clan using hereditary magical powers in the fight.