After being nabbed while trying to stow away on board an ocean liner en route to Hawaii, young Bobby Breen sings for his travel fare and, along with sidekick Pua, turns detective to recover stolen naval documents from crooks

When ocean liner stowaways Billy Coulter and Pua, a young Hawaiian, are caught in the cabin of Strings, a songwriter and ship musician, Captain O'Hare tells the orphan Billy that he will be sent back to San Francisco as soon as the boat docks in Honolulu. Although Billy's singing abilities impress the captain, he remains adamant about returning him, and consequently, when the ship lands, Billy and Pua dive overboard and swim to freedom on shore. In Honolulu, Pua takes Billy to his sister Hina, who shields him from the police. Concerned for Billy's safety, Hina then takes the boys to Maui, where Aunty Pinau lives, and is joined by Strings, who has violated his rule about not setting foot on the islands he writes about in order to search for the stowaways. After a few idyllic days on Maui, Billy is spotted by Navy commander Joe Milburn and his wife, former passengers on O'Hare's ship who are visiting the well-to-do Harlows. Unknown to Milburn, a group of foreign agents are plotting to steal secret government papers from him with the help of Julius, a trusted Harlow servant. That night, at Aunty Pinau's annual luau, Milburn confronts Billy and convinces him to return to Captain O'Hare to clear his name. On his way to the marina, Billy and chauffeur Julius are stopped and questioned by police about Milburn's stolen papers. Billy, remembering a conversation he overheard while exploring a cave with Pua, realizes that Julius is the thief and escapes from the car. Eventually, Billy and Pua lead Milburn and the police to the spies and are hailed as national heroes for their efforts. Billy then sings farewell to Hawaii as he and the Milburns set sail for San Francisco.