Victor Conway, a West Indian dockside worker, is a member of the Caribbean Centre, run by the forthright but kindly Miss Trevor. When Victor breaks the exciting news that his girlfriend Violet is coming from Trinidad to visit him, his spiv compatriot Joe Martell boasts that he will take her away from Victor. A fight ensues, but it is immediately stopped after the intervention of Mathew Johnson, the local pawnbroker and a friend of Miss Trevor's.

Later, a sailor gives Joe a packet of cigarettes to deliver; when Joe realises that he is closely watched by the police he phones 'the boss' to ask for help and goes into hiding by the wharf. Victor spots him climbing down to the foreshore and, suspicious, follows him. They quarrel again but this time they are interrupted by a gunshot that kills Joe. Terrified that he will be accused of the murder, Victor runs away.

The next day, Danny, a Cockney newspaper boy, finds the cigarettes while out beachcombing and takes them home, hoping to sell them later to help pay for the watch he has seen in the window of Mr Johnson's shop. On the way, he is chased by older boys and takes refuge in an old loft. As he ascends the rickety old ladder, one rung gives way, but before he can fall he is grabbed by Victor, who has been hiding there. Hearing Victor's story, Danny takes pity on the scared and worn-out man and offers to help him.

With the police on Victor's trail, Danny sneaks out of the house with some food for the fugitive. However, he is pursued by his grandfather, who realises that something is afoot. With the help of his grandfather, Danny takes Victor back to their junkyard home. Victor agrees to go to the police to claim his innocence once he has had a chance to explain himself to Violet. Danny and his grandfather meet Violet at the station the following day and explain to her what has happened, but when they return home they find Victor gone; the police have found his hideaway abandoned. Danny's grandfather denies all knowledge.

Although Danny again finds Victor, he meets a hostile reception, for the wanted man assumes that Danny betrayed him to the police. Danny is further puzzled when he finds his packet of cigarettes missing. He soon learns that the Police Inspector took them and that they contain narcotics.

Delivering papers, Danny notices that Miss Trevor has a packet of the same cigarettes. When asked by Danny's grandfather, Miss Trevor explains that she gets them from Mr Johnson, who buys them from sailors. Danny has another shock when he sees a sailor, with a packet of the cigarettes protruding from his pocket, go into Johnson's shop. Peeping through a side window, Danny sees the sailor offer Johnson the gun which he knows killed Joe; Johnson gives the sailor £100 in exchange. As Danny tries to flee, he makes a noise, alerting Johnson to his presence. The pawnbroker grabs Danny and drags him inside, where he reveals that not only did he kill Joe, but he also runs a drug-smuggling racket. Johnson is putting a bound and gagged Danny into the back of his van when he is interrupted by Miss Trevor. Although he manages to get rid of her, her suspicions are aroused; they are confirmed when she discovers a clue which Danny has left. Miss Trevor phones the police and, running into Victor and Violet, also tells them about Danny's abduction. Knowing Johnson has a boat at the wharf, Victor arrives there almost at the same time as the pawnbroker.

As the police arrive and help Danny to safety, Victor skilfully operates a crane and causes a mountain of oil drums to descend upon the helpless Johnson.

At a party that night at the Caribbean Centre, Victor presents Danny with a new watch.