May 8, 1938

A steamship, the Amazon, is headed to some South American country called "Rikiguana". The captain of the Amazon does not know that there is a group of revolutionaries aboard who are smuggling arms to the rebels in Rikiguana in crates that are labeled as refrigerators. As the ship nears land the revolutionaries get a coded message from an unnamed general. The message reveals that their scheme has been discovered and that they must blow up the Amazon, and kill everyone on it, to prevent the weapons from falling into the hands of the government.

Also on board the boat are Lamont Cranston and Margo Lane, who are on a pleasure cruise. After the captain has Lamont put in the brig for demanding an investigation, The Shadow springs into action.