Born in 1821 in Ohio, Wallace moved with his family to Illinois in 1834, where he was educated at Rock Springs Seminary in Mount Morris. On his way to study law with Abraham Lincoln in Springfield in 1844, Wallace was persuaded by local attorney T. Lyle Dickey, a close friend of Lincoln, to join his practice in Ottawa instead. Wallace eventually married Dickey's daughter, Martha Ann, in 1851.

When the Civil War broke out, both Wallace and Dickey immediately volunteered for service with the Eleventh Illinois, which assembled in Springfield. Wallace was appointed brigadier general for his performance at Fort Donelson, the first notable Union victory in the Civil War; his troops had saved the day, although the Eleventh Illinois had lost nearly two-thirds of its men. He then moved with his troops to Pittsburg Landing, Tennessee, where Confederates launched a surprise attack on the forces of Major General Ulysses S. Grant at Shiloh Church on Sunday, April 6, 1862. Wallace, who held only temporary command of one of Grant's six divisions, fought bravely but was mortally wounded as he began to withdraw his men on the afternoon of the battle.

Isabel Wallace traces her father's life from his upbringing in Ottawa through his education, his service in the Mexican War, his law practice, his courtship of and marriage to her mother, and his service in the Eleventh Illinois until his mortal injury at Shiloh. Based on the copious letters and family papers of the general and hiswife, the biography also provides historical information on federal politics of the period, including commentary on Lincoln's campaign and election and on state politics, especially regarding T. Lyle Dickey, Wallace's father-in-law and law partner, prominent Illinois politician, and associate of Lincoln.