Millie, the Bing family's dog, is very lonely in the house by herself all day. The Bings are always busy and Millie wonders where they go to every morning. She is determined to find out and, now that she is so thin because she has been too lonely to eat her biscuits, she discovers that she can get out through the cat flap. She looks behind the compost heap, outside the garden and even Somewhere Else, but instead of finding the Bings she gets lost. Millie is rescued by a little boy called Billy and soon has two homes – a daytime one and a night-time one and is never lonely again.