The dog Rover plays with a baby in front of the fire. In the afternoon, the baby is taken out by her nurse. A beggar woman asks the nurse for money, but she refuses. The nurse then has a romantic assignation with a soldier, which causes her to take her eye off the pram, and the beggar woman takes advantage of this by stealing the baby.

The nurse goes to the baby's mother and tells her what has happened. Rover, after listening intently, jumps through the window and races down the street, around a corner and across a river. He finds a collection of slum dwellings and goes from door to door.

Finally hitting upon the right one, he enters, finding the beggar woman removing the baby's clothes. She shoos him away, so he returns home and pleads with the baby's father to accompany him. He follows Rover in a boat across the river, and Rover leads him to the beggar woman. The baby is rescued and returned to his mother. Rover skips happily around them.