Early one morning the experienced chimney-sweep Black Bob sets off to work with his son and assistant Clem. For the first time, they are accompanied by the eight-year-old Sam who must start working because his father is ill. Clem, Bob and Sam, who is crying in terror, arrive at Iken Hall. As she meets them, Miss Baggott the housekeeper feels sorry for the lad, but the sweeps convince her that Sam will get used to it and learn to love his trade, and his toys will soon be abandoned in favour of brooms. A rope is wound round the lad and he is sent into the chimney.
The children of Iken Hall and their guests are playing hide-and-seek. One of the girls - Juliet - hides under a sheet that is covering a chair. She is joined by Johnny. Suddenly a frightened voice comes from the fireplace; Sam has become stuck and is calling for help. The children tug at the rope and soon the little sweep is in the room. Sam complains that he doesn't want to sweep chimneys and asks the others to protect him. To start with, it is decided to hide him in a cupboard. But to throw the adults off the scent the lad is led to the window – on the way he leaves black marks – and then he is carried to the cupboard. The ruse has succeeded: Miss Baggott and the sweeps decide that Sam has run away, and they depart to search for him.
The children entrust their secret to Nanny Rowen and ask her to wash and feed the lad. It transpires that the nanny knows Sam's father as they come from the same district. She agrees to help the lad escape: the next day she and the guests will be going home, and she will hide Sam in a large trunk. The despairing Miss Baggott returns, and she asks all the toys be packed away in the trunk. But Sam is hiding inside! Juliet screams and faints to distract the housekeeper's attention.
The next morning Juliet gives Sam some money. It is time for the guests to depart. But Tom the coachman and Alfred the gardener are unable to lift the leaden trunk and ask for it to be unpacked. The children offer to help. The clothes are transferred into the carriage, the guests bid farewell and depart, taking little Sam with them away from Iken Hall.