When his father is killed fighting for the Union in the War Between the States, thirteen-year-old Tom Carroll must take a job to help support his family. He manages to find work at a bustling ironworks in his hometown of Brooklyn, New York, where dozens of men are frantically pounding together the strangest ship Tom has ever seen. A ship made of iron. Tom soon learns that the Union army has very important plans for this iron ship called the Monitor. It is supposed to fight the Confederate “sea monster”—another ironclad, the Merimac. But almost no one believes the Monitor will float!

Meanwhile, Tom’s job at the ironworks has made him a target of Confederate spies who offer him money for information about the ship. Tom finds himself caught between two certain dangers: an encounter with murderous spies and a battle at sea in an iron coffin. . . .