Emily and Alexander travel to Scotland, where their cousin Angus is waiting for them. Angus is Robby's mouse, who lives with his parents in a castle on Loch Ness. For some time, however, the castle has been haunted. Every night a ghost is haunting the place, so Robby's parents want to sell the castle. Emily and Alexander are able to prevent this, as they convict the neighbor as the culprit. There has been a family feud between the two families for centuries, as gold is said to be hidden in Robby's parents' castle.