The Hardy brothers embark on a freighter trip under mysterious circumstances and find themselves involved with a smuggling ring.

A strange substitute -- The three cornered scar -- Suspicion -- No passengers -- More disappointment -- The Morton special -- A weird tale -- Missing letters -- Code numbers -- Frank in trouble -- Stolen tickets -- Harrowing experience -- "Mrs. Harrison" again -- Spy in the shadows -- The abandoned farm -- Success and failure -- Danger at the carnival -- "You'll never come back!" -- Crowfeet -- Captured!