Grey DeLisle returns voicing Daphne and remains as such from here through the rest of the franchise so far. Its also the first time Mindy Cohn voices Velma in the films after first assuming the role in What's New, Scooby-Doo?. She would remain in the role until 2015.
Mystery Inc. travels to Loch Ness in Scotland to see the famous Blake Castle, where Daphne's cousin Shannon lives, and where the Highland Games are being held. But there's a problem. Apparently, there was a recent attack made by none other by Nessie herself. Shannon also claims to have seen the creature before, and claims that it is real, siding with local enthusiast Del Chillman and Professor Pembrooke, a scientist who staked her whole career on proving the monster's existence. However, Sir Ian Locksley, the head judge of the games, thinks just the opposite, causing a mutual hatred between him and Pembrooke.
The next night, Shaggy and Scooby are chased by the monster, ruining the game field in the process. The gang searches the area for clues, and sure enough, they discover that the monster tracks lead into town instead of toward the loch. Whether they like it or not, they've got a mystery on their hands.
This film contains examples of the following tropes:
- Bookcase Passage: There's a bookcase that's really a secret passage in Blake Castle.
- Conspicuous CGI: The Loch Ness Monster itself is clearly made using CGI.
- Cool Boat: Sir Ian Locksley's got an impressive boat. Professor Fiona's as well if you count the fact that it has a Nessie submarine docked under it.
- "Could Have Avoided This!" Plot: The person behind the fake monster only wanted to try and make Sir Ian believe in a real one, and did the whole scam instead of just showing Ian the very good photos they seem to have of the "real" monster. After the hoax is revealed Velma prods them into sharing the photos... and Ian is instantly hooked.
- Earworm: "You take the high road, and I'll take the rocky road! Like, rocky road ice cream, that is!"
- Everyone Is a Suspect: Pretty much everyone short of Shannon is given some reason to potentially be behind a fake monster:
- Professor Pembroke would want more people to believe in the monster in general to help her research. In reality she just wanted to make a believer out of Ian, frustrated with his cynicism.
- While he doesn't seem to have a motive, Sir Ian clearly has the funds to create the sort of aquatic machinery needed to fake the monster and shows up very eager to hunt it down. He just wanted to end the hoax and stop the threat to the games.
- Dell Chillman thinks the games are making Nessie angry and causing other problems, so the gang think he may be behind the monster to scare people off. He's not, though his van is stolen and used in the hoax.
- Colin and Angus would want to potentially scare away competition from the games. They don't really care about the games but were involved anyway because they thought it was a good prank.
- Mr. Haggart wants more people to believe in Nessie because it will increase business for his inn. He's not involved with the hoax at all.
- Duncan MacGubbin is cryptically creepy and seems to have some odd warnings about the Blake Castle... Nope, he's just a normal creepy guy.
- Everything's Louder with Bagpipes: Naturally, for a film set in Scotland. They show up at the Highland Games at the end.
- For the Evulz: Colin and Angus only help the culprit with their scheme because they think it's a good prank.
- Glamour Failure: The monster that was made out of Dell's van and chased the gang on land goes from terrifyingly realistic like the one in the water to obviously just a cheap costume on a vehicle once the chase scene is over.
- Haggis Is Horrible: Not even Scooby and Shaggy will give haggis a try.
- Lots of Luggage: Daphne. Lampshaded at the end.Shaggy: Maybe next year there can be an event called "the long-distance Daphne Blake suitcase carry"!
- Meaningful Name: Del Chillman is a hippie.
- Monumental Damage: The monster knocks a tower clean off Blake Castle at one point, with Shaggy and Scooby inside it.
- The Mutiny: Sir Ian's crew turn out to have ambitions of their own and try to catch the monster for themselves, interfering with the gang's trap.
- Mythology Gag:
- The gang dealing with the Loch Ness Monster had been done before in the 1972 The New Scooby-Doo Movies episode "The Loch Ness Mess" with the Harlem Globetrotters.
- Daphne's cousin Shannon describes the Blake family as being "danger-prone" and having a history of falling into all sorts of traps. "Danger-prone Daphne" is classic in-series nickname due to how often she was captured or trapped.
- New-Age Retro Hippie: Del Chillman is a lot like a hippie.
- Nothing Is Scarier: The Wham Shot of Scooby potentially seeing the real Nessie as they drive away from Blake Castle seems to indicate that the gang was dealing with the real thing on at least a few occasions throughout the movie. There's no way of knowing which attacks were just staged and which ones were where lives were actually in danger.
- The Prankster: Colin and Angus like to play practical jokes. This is how Fiona got them involved in the plot.
- Real After All: At the end of the movie, when the Mystery Gang is driving off, Scooby notices a large, Nessie-like creature swimming in the lake nearby before diving underwater, leaving him bewildered. It is possibly the real monster.
- Red Eyes, Take Warning: The monster has red eyes.
- Road Sign Reversal: When Shaggy and Scooby are driving around in the Mystery Machine, someone pulls the "switch two signs" trick on them, sending them into a swamp.
- "Scooby-Doo" Hoax: Three fake monsters - one that chases Shaggy and Scooby at Blake Castle at the start, and later chases them into a pit (it turns out to be Colin and Angus); Professor Pembrooke's mini-sub that chases them in the loch; and Del's van when it's made out to look like a monster.
- Shout-Out: The Loch Ness Monster's design in this film is almost identical to the Paleosaurus. Both films were from Warner Brothers.
- Stock Ness Monster: It's the real deal. Well, actually, one is a submarine and one is Del's van, but there's potentially a real one too.
- Sub Story: The gang travels into Loch Ness in a sub to explore underwater caves.
- Walk on Water: Shaggy and Scooby manage to run on water using oars.