Based on a novel by Claude McKay, a big African finds a run-away English boy and becomes his friend.
In Marseilles Joe (Paul Robeson) sings "Lazin'." On a ship Mrs. Oliphant (Joyce Kennedy) and her husband Ferdy Oliphant (Eric Cowley) tell police that their son Gerald has been kidnapped. Policemen take Joe to the prefect, who asks for his help. Mrs. Oliphant offers 5,000 pounds reward, and Joe says he won't talk about it. He looks at kids, and soon his friends Chuck (James Hayter) and Corney (Lawrence Brown) find out about it. At the Cosmo Cafe Manda (Elisabeth Welch) sings "One Kiss." Joe follows Spike (Roy Emerton) because he is carrying milk; but Joe, Corney, and Chuck find a cat. Spike announces that Joe is helping the cops look for a kidnapped boy.
Joe sings "Roll Up, Sailor Man." He finds Gerald Oliphant (Eldon Gorst) swimming and carries him to Manda's place. Gerald says he ran away, and Manda gives him clothes. Gerald threatens to get them in trouble if they take him back; he wants to stay with Joe and Manda. Joe shows Gerald how to box. Joe sings Gerald a lullaby, and after a prayer he is put to bed. Manda warns Joe he is kidnapping and goes to sing. Joe sings a French song and tells two policemen that he has not seen the boy, while Gerald is hiding. At the cafe Marietta (Marcelle Rogez) meets Joe. Manda tells Joe that Gerald is gone. She sings "Harlem" while Gerald hides under tables and goes to Joe. When the lights go out, Spike grabs Gerald and takes him to the police. Gerald says that he was not kidnapped. Spike gets 50,000 francs reward from Ferdy Oliphant. Joe comes in, and Gerald sides with him. Spike offers Joe half and takes him to Marcelle's place. She invites Joe to go out with her and Spike; they drink. Joe calls on Manda late and has a hangover. Manda is angry at Joe and makes him leave.
The ship doctor tells Gerald they are sailing tomorrow. The doctor advises the Oliphants to get Joe to visit Gerald. Joe and Gerald talk. Gerald gives Joe food and eats too. Joe advises Gerald in poetic verse. Joe declines money from Ferdy Oliphant for seeing his pal. The Oliphants ask Joe to go with them for pay. Ferdy Oliphant and Joe drink and say good-bye at the cafe. Manda sings "One Kiss," and Joe leaves. In the final scene Joe watches the ship depart with Spike in black face saying he was kidnapped. Manda offers her big fella Joe breakfast, and they walk off together.
Joe's voice and buoyant personality charm the boy seeking adventure away from his over-bearing parents. Joe gives up money and risks legal consequences because he has been "kidnapped" by Gerald, showing great love. Yet he chooses to stay with Manda, who also loves him.