The Mystery, Inc. gang travel to
Loch Ness to see Blake Castle, home of
Daphne Blake's Scottish ancestors and her cousin, Shannon Blake, for the upcoming annual
Highland games. Upon their arrival, Shannon informs them that the castle has recently been terrorized by the
Loch Ness Monster. Along the way, the gang encounter
Del Chillman, a Loch Ness Monster enthusiast and amateur
cryptozoologist; Professor Fiona Pembrooke, a scientist who has staked her scientific career on proving the monster's existence; local competitors and brothers Colin and Angus Haggart; their father Lachlan; and Sir Ian Locksley, the games' head judge, a rival of Pembrooke's, and director of Scotland's natural history museum who firmly believes the monster does not exist. Later that night,
Shaggy Rogers and his dog
Scooby-Doo head to the kitchen, but are chased by the monster, destroying the playing field in the process. The following morning, an enraged Locksley orders Shannon to repair the damage while
Velma Dinkley discovers monster tracks that lead towards a nearby town instead of the loch. While the Haggarts repair the field, the Blakes, Velma, and
Fred Jones take Pembrooke's boat to search the loch while Shaggy and Scooby use Mystery Inc.'s van, the Mystery Machine, to search by land. However, both groups are simultaneously attacked by the monster. Upon their return, the gang learn Locksley is conducting his own search via a high-tech ship to prevent any further "peculiarities" from disrupting the games. Using his sonar equipment, the gang find something deep in the loch. They take Locksley's
minisub to investigate, but are attacked once more, during which a camera gets broken off before Locksley's crew rescues them. The gang later learn Chillman's van was stolen before being attacked a third time, only to learn their pursuer was Chillman's van dressed up as the monster. Fred sets up a trap to capture the real monster before sending Shaggy and Scooby out on the loch to act as bait. Complicating matters, a heavy fog bank rolls in, blocking visual contact with the pair while Locksley's crew mounts a mutiny and captures him, the gang, Shannon, and Chillman, intending to capture and sell the monster. As Shaggy and Scooby are attacked, Fred and Chillman are pulled into the water by Fred's net trap while the Blakes stop the mutineers and capture the monster with the ship's magnetic claw. Suddenly, a second monster emerges and chases Shaggy and Scooby, only to fall into a pit trap the gang previously set up. The first monster is revealed to be a modified submarine operated by Pembrooke, who hired the Haggart brothers to operate the second monster, a huge puppet. Velma deduces Pembrooke concocted the scheme to convince Locksley of the monster's existence and enlist his aid in finding it. The next day, as the games get underway, Locksley calls everyone to his ship to review pictures of what appears to be the real Loch Ness Monster that the detached camera took, which came from a depth far below that even Pembrooke's submarine could not operate at. Finally convinced that the monster might be real, Locksley invites Pembrooke and Chillman to help him investigate further. As Mystery Inc. leaves Scotland, Velma observes "maybe some mysteries are just better left unsolved" while Scooby glimpses the monster swimming by. ==Production==