That Little Square Box

Mr Hammond is on his way to America when he overhears two passengers discussing a suspicious plan that is going to be executed at 10 o'clock in the evening. The two unknown passengers boarded at the very last minute. Their baggage was not searched. And their plan consisted of some mysterious box. What do you think happened that evening? Did Mr Hammond try to warn the rest of the crew, or did he escape in a lifeboat? Could it all be a big misunderstanding, or will the American steamer be blown up?