When the son of the owner of a shipping line is given a secret letter by his father, he thinks nothing of it as he enjoys the privileges of his wealth on the journey to Shanghai. The thing is, though, someone else is determined to know about the contents of the letter and "Bob" (Thomas Beck) quickly finds himself at the centre of quite a conspiracy. Fortunately, the enigmatic "Moto" (Peter Lorre) also happens to be travelling, incognito of course, on the same boat and he recognises a tattoo on the steward's arm as that of a killer he'd encountered before. Whilst "Moto" is working to find out wh...