Hugo specializes in coming up with nasty schemes, but this time he’s outdone himself. He designs a huge mechanical monster capable of swallowing up the dragon. Merlin builds a prototype which wreaks havoc in the castle and comes perilously close to flattening Riri, Melody and Harry. Armed with picks and shovels, they’re busy poring over a mysterious map in search of buried treasure… with which they hope to impress the king. But each of them wants to be the first to find the treasure, and as they work feverishly, the castle becomes riddled with holes. Meanwhile, Hugo’s mechanical monster looks like it may just succeed in obliterating the dragon…