In the broom cupboard of a small dwelling called 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. Tumtum and Nutmeg have a wonderful life but the children who live in Rose Cottage, Arthur and Lucy, are miserable. So, one day Tumtum and Nutmeg decide to cheer them up ... Tumtum repairs the electric heater in the attic where the children sleep and Nutmeg darns the children's clothes. Arthur and Lucy are delighted and think a Fairy of Sorts is looking after them. But then Aunt Ivy with her green eyelids and long arms arrives. She hates mice and hatches a plan to get rid of them. Soon Tumtum and Nutmeg are no longer safe to venture out ...