In addition to bringing alive America’s war for independence, including information on the first submarine built in America, After working as spies to aid the Colonies and delivering a message to General George Washington himself twins Ambrose and John Clark find themselves volunteering for another mission to help the newly forming United States. This time, 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. But the biggest challenge may be finding a way to free their imprisoned older brother.