cooby-Doo, Shaggy, and the Mystery Inc. crew travel to Scotland on vacation and find themselves unexpectedly tackling their biggest monstrosity ever: the Loch Ness Monster! Does it really exist? Early evidence suggests a scary "yes" when something gigantic appears outside the window of Daphne's ancestral family castle. Will Scooby-Doo and crew solve one of history's longest-running mysteries?

Overview from themoviedb.org