A girl named Lex is arrested after trespassing on the land surrounding the huge medical centre where she's kept captive under maximum security. Mark and Song Li learn that the girl is an extraterrestrial trying to return home. Her ship lost fuel during their journey through space, and they travelled on Earth to collect their fuel, which is water. They intended to land in the ocean, but accidentally crashed near the centre. Lex wants to go back to the ship to return home, so the teens try to help her escape.