Mary-Kate and her granny are going to stay at a very quiet castle near a very quiet loch in the Scottish village of Bonkillyknock. The perfect destination for reading beside fireplaces and drinking cups of tea with Granny's friends. However, this is no ordinary holiday - it's the 93rd World Society of Monster Hunters' Conference! So, when an ear-shattering howl interrupts the convention, Mary-Kate isn't too anxious. After all, the experts are on hand to investigate. But when the castle kitchen is destroyed and everyone suspects the usually peaceful Loch Morgavie monster, Mary-Kate isn't sure the clues add up. Could there be some other beastly problem bothering Bonkillyknock Castle? It's up to Mary-Kate to find out...