Jack and Annie are sent back in time by the librarian Morgan le Fay to help find a specific piece of writing for her library. They land in colonial Pennsylvania on a cold, snowy Christmas Eve in 1776. There, they encounter General George Washington and his weary troops as they prepare to cross the icy Delaware River for a surprise attack on the Hessians at Trenton. When the mission is nearly thwarted by low morale and the brutal weather, Jack and Annie use their knowledge of history and a mysterious letter to encourage Washington to complete the crossing. The story blends historical facts about the American Revolution with the series’ signature time-travel fantasy, teaching young readers about leadership and the birth of a nation.