In the broom cupboard of a Rose Cottage, stands a house fit for a mouse - well, two mice actually. A house made of pebblestone, with gables on the windows and turrets peeking out of the roof. A house with a ballroom, a billiard room, a banqueting room, a butler's room and a drawing room. The house belongs to Mr and Mrs Nutmouse, or Tumtum and Nutmeg as they affectionately call each other.

When General Marchmouse unexpectedly joins the Nutmouses on a camping trip things soon begin to go horribly wrong. Before they know it, the mice are whisked downstream on Arthur's toy boat, Bluebottle. The General soon spies an island in the distance that he is determined to explore - and fiddlesticks to anyone who disagrees! But once ashore the mice soon find that they are not the only ones to have discovered the island . . .