In this second book in the American Revolutionary War Adventure series, twins Ambrose and John Clark find themselves volunteering for another mission to help the newly forming United States. Inspired by their success in delivering a secret message to General George Washington himself, the boys step up to help transport much-needed gunpowder to the patriots and end up in an even more dangerous situation, trying to man one of the first submarines and then, later, attempting a prison break to rescue one of their older brothers.
