The Gang infiltrates a WW2 German underwater robot facility off the California Coast.
A robot disguised as a Nazi World War II soldier attacks Cassidy Williams at her radio station, eventually self-destructing as Cassidy fights back, taking the entire building with it. She explains to the gang that these robots have been attacking her for the past week. Robots continue to attack the gang as they investigate. When the gang realizes that the robots are coming from deep underwater, Daphne recruits two of her babysitting charges, Tom and Tub, and their seal (also named Scooby), to transport the gang in their submarine to the robots' spawning vats, in an area the kids call "The Midnight Zone". Shortly after submerging, the sub is attacked by a group of robots and damaged, and the gang stumble upon an underwater base and attempt to use it to repair the sub, only to discover that the base is the factory where the robots are constructed, run by Professor Pericles. In the end, Pericles escapes leaving the laboratory to self-destruct, seemingly killing Cassidy Williams as the gang, Tom and Tub, and Scooby the Seal escape.