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, going for long walks in galoshes and drinking cups of tea with Granny's old friends. At least, that's what Mary-Kate thinks. However, this is no ordinary reunion - it's a 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 turned upside-down and the experts suspect the usually secretive Loch Morgavie monster, Mary-Kate isn't sure the clues add up. Could there be some other kind of beastly problem bothering Bonkillyknock Castle?