Best friends Anne Ferguson and Julie Sawyers are on a class field trip to the Aquarium in Baltimore’s Inner Harbor when Anne suddenly disappears. Looking for her friend, Julie enters a dark room filled with deep-sea creatures…and a bony hand grasps her ankle! The hand belongs to a ragged girl named Millie, who claims to be running north to escape a notorious slave catcher. Before Julie can learn more, Millie has fled. Julie chases after her – and is stopped by the vision of a ghostly wooden ship that seems to be suspended above a modern-day touring boat. What is going on?

Meanwhile, Anne has somehow been transported back in time, and is being held captive as a thieving gypsy in the year 1849! Now, together, all three girls must join forces across time and history to save each other from a terrible fate. Can they all escape to freedom before it’s too late?