Henry is awake in hospital after having had an operation, and he is worried about his pet mouse, who is sick at home. To his astonishment, he sees lights behind the skirting boards, and suddenly doors open and a whole hospital for mice invades the ward. All sorts of things are wrong with the mice, but the 'Emergency Mouse' is Champion Mouse, the cheese-stealer. He has had his tail caught in a trap. Dreadful things almost happen to him, but he always wins through. In the morning Henry wakes up, to be told that he will go home that day and that his pet mouse is well again. Zany cartoon drawings and a fun story line.