When Velma's uncle Dave goes missing, the gang attempts to find him. On their search, the gang is attacked by the legendary Willawaw, which is said to capture people if an owl calls their name.
While on a boat flowing down the Gulf Stream, the gang witnesses a flying saucer hijacking an airplane. They crash on Diablo Island, where they discover a spooky-looking sea captain and a trio of one-eyed and skeleton extraterrestrials.
The gang travels to Scotland to visit their friend Aggie MacDuff, whose family castle is being plagued by the ghost of her great-grandfather, who lures the Loch Ness Monster with his bagpipes.
