On the night of the Fourth of July at the Delaware County Home for the Aged, Louisa McLain, the oldest resident of the nursing home, turns on her nightlight and opens a box of neatly stored letters from 60 years in the past. The first letter is from her son, George, telling her that he and his friend, Chester Gerber, have left to volunteer for the Union army in the opening months of the Civil War. Corrinne Miller, a nurse, finds Louisa perusing the letters and sits with her, reading each one out loud while Louisa listens. They tell bits and pieces of the story of the war, but what really happened is another matter.

A Call to Arms will transform you back to July 4, 1861, when George and Chester are befriended by a radical abolitionist minister, Reverend James Franklin Turner. The three of them are attached to the Indiana 19th Volunteer Infantry that forms a part of the famed Iron Brigade. As the war ramps up, they are involved in some of the bloodiest battles of the war. But they become more than soldiers. The three of them are recruited to form a spy ring, slipping across the Confederate lines to gather key information. Their missions are harrowing and, as it turns out, more than just spying. They meet Jessie Smith, a conductor on the Underground Railroad.

Follow the perilous experiences of George, Chester, Jessie and Reverend Turner. When they are not fighting, their spying and slave running put them in life-threatening situations full of twists and turns. All the while, Louisa McLain is waiting at home for the next letter to arrive.

A Call to Arms is based on the first book in the Fourth of July Trilogy by Kevin Yaney.