After the ship docks in London, bank officials come on board to remove the gold. Everything seems normal, and the watch is in place, but when the door into the bullion compartment is opened, the first mate on guard inside is found to be dead, again of no apparent cause. When the bullion is removed, all seems in order, until the bank reports that all of the chests actually contain lead! As additional cargo is unloaded, an especially heavy case arouses the second mate's suspicion, and he has the man operating the crane "accidentally" drop a case. It bursts open, and chests of gold bullion are found. An elaborate plot is revealed, in which conspirators brought aboard identical chests containing lead, stored in other cargo; the special compartment to hold the bullion was built with a sliding door and connection to a secret passage. In the dead of night the thieves gradually swapped the chests. To avoid detection by the guard inside the compartment they used a narcotic gas. Too low a dose allowed the second mate to awaken and see the chests missing; but too high a dose killed the first mate. The same narcotic gas evidently killed the previous captain, who was gassed to keep him from learning too much about the theft going on directly beneath his cabin.