As a punishment because he rebels at working with Merlin's pigeons, Squire Brian is sent on an errand to deliver a crate of pigeons to a neighboring castle. En route, he becomes involved with a gang of thieves who stole the precious Ruby of Radnor.

King Arthur learns that a nearby village is being terrorized by a horrible monster. Sir Lancelot is sent to investigate. He discovers that the monster is really a Viking boat, and that it's the Vikings who are doing the terrorizing.