Marlow arrives at an empty, dilapidated house and goes upstairs to a room newly furnished as a nursery. He unpacks his parcels: milk, sweets and a golliwog. Slitting open the golliwog, he puts a bomb inside.

A car pulls up outside a large house. Inside the house, Jonathan Chester, dressed in a school uniform, runs round. He says goodbye to his father and gets into the car. The nanny asks Marlow, who is driving the car, where the usual driver is and is told he's gone to the dentist. The driver goes to the rundown house and takes the boy upstairs to the nursery. He gives him the golliwog and the boy remarks that it's ticking. Meanwhile, Jonathan's school rings Mr Chester and the nanny is told that Jonathan has not arrived. Marlow then rings Chester and tells him he has Jonathan. Marlow locks Jonathan in the nursery and goes to Chester's house.

Once there, he demands £50,000 for Jonathan's return. His plan is to take the money and fly to Rio, from where he will phone Chester and tell him where Jonathan is. Meanwhile, the nanny phones the police.

At Scotland Yard, Parnell is interviewing a criminal who is refusing to name his accomplice; Parnell breaks him and he talks. He is then called to Chester's house to find that he has gone to the bank to fetch the ransom money. Parnell confronts Marlow; he wants to arrest him and get him to talk, but Chester wants him set free. Chester calls his friend, Assistant Commissioner Bewley of Scotland Yard, who comes to the house and orders Parnell to let Marlow go. Parnell and Bewley argue and Parnell eventually wins, Bewley making him personally responsible for Jonathan's safety.

Parnell arrests Marlow and begins interrogating him, trying to find out about his childhood. It seems as if Marlow is about to crack and tell Parnell where Jonathan is when Chester storms in.

Marlow and Chester are left alone in the drawing room. Marlow taunts Chester with the prospect of his son's death and Chester lunges at him. In the struggle, Marlow falls to the floor and hits his head. He is taken to hospital with concussion where the doctor declares that he needs an operation but is too weak.

While Chester sits by Marlow's bed, waiting for him to regain consciousness, the investigation into the kidnapper's identity continues. Night falls and Jonathan gets into bed with the golliwog.

A lead takes Parnell to The Golliwog Club where they find Marlow's parents, who run the basement dive. But they have little contact with their son and can offer no useful information.

At 5.30 the next morning, Marlow dies. Commissioner Bewley tells Parnell he's very unhappy with the way the case has been handled.

Later that morning, an estate agent runs into his office and calls the police, having recognised Marlow's photo in the paper. The police arrive and bundle his colleague into a car to take them to the house Marlow rented. At the house, Jonathan gets up and washes his face; he then baths the golliwog in the sink, just as the clock strikes ten. The police arrive only minutes afterwards and bundle Jonathan out of the house. Parnell sees the golliwog in the sink and realises that the boy saved himself by deactivating the bomb.