When their school bus veers off course while taking the kids from Gravelmuck Elementary on a field trip, monster detectives Tank and Fizz witness a crime that brings them snout to snout with Rockfall Mountain's oldest monster, the ancient dragon Firebane Drakeclaw. Thieves have stolen the Crown of Peace, which keeps the monster clans of the Dark Depths from fighting, and Tank and Fizz saw the whole thing. Now the detectives must track down the thieves and find the crown or their whole class will become dinner for one very hungry dragon!