Young Lex Simms is half-alien. Like the rest of his family he has inherited the remarkable Martian abilities of changing shape and traveling in spirit form through time and space. Lex risks his life to rescue the Martians from their doomed planet and brings them to Earth, only to have a violent storm nearly kill them. The older Martians plead with Lex to take them back to Mars where they expected to die of thirst anyway. The younger ones, however, want to stay on Earth and become human. Meanwhile, arch-enemy Fi detects their presence, and - oh boy - is he mad. According to an agreement made eons ago, Earth belongs to Fi. He threatens to torture any non-Earthling who dares to step foot on his planet. The Martians must choose whether to return to Mars where death awaits, or stay on Earth and face Fi's terrible anger. Either way, their future looks grim.