The Killer Angels tells the story of the Battle of Gettysburg. On July 1, 1863, the Army of Northern Virginia, or Confederate army, and the Army of the Potomac, or Union army, fought the largest battle of the American Civil War. When the battle ended, 51,000 men were dead, wounded, or missing. All the characters in the novel are based on real historical figures. They include General Robert E. Lee, commander of the Confederate army; General James Longstreet, Lee’s second in command; and Union Colonel Joshua L. Chamberlain, who participated in one of the most famous segments of the Battle of Gettysburg, the fighting on Little Round Top.

The story begins on June 29, 1863. A spy comes to Longstreet and informs him that he has seen the Union army moving nearby. This information surprises Longstreet, because General J. E. B. Stuart is supposed to be tracking the Union army with his cavalry. Longstreet thinks the Confederate army must quickly move north to intercept the Union. The Confederates swing southeast through the mountains and toward a small town called Gettysburg.

Miles south of Gettysburg, Union Colonel Joshua L. Chamberlain awakes to discover that his regiment, the Twentieth Maine, has a hundred new members—mutineers from the Second Maine. Chamberlain gives them a brief speech, asking them to continue to fight, and all but six of the men join the Twentieth Maine freely.

In Gettysburg, General John Buford, leader of the Union cavalry, rides into the town and discovers Confederate troops nearby. He realizes that the two armies may end up fighting in the town, so he takes his two brigades—approximately 2,000 men—and positions the soldiers along the hills in the area. He knows that having high ground is the key to winning the battle, since it is easier to fight from above than below. In the Confederate camp, Longstreet meets with George Pickett and several other generals.

On the morning of July 1, Lee rises and curses Stuart’s absence. He is blind without Stuart, because without him he has no idea where the Union army is. He meets with Longstreet, who wants to swing southeast and come between the Union army and Washington, D.C. Then, Longstreet says, the Confederates can use defensive tactics and have a much better chance of winning the battle. Lee refuses, because he wants to smash the Union army aggressively in one decisive stroke.

Meanwhile, the battle begins at Gettysburg when the Confederates attack Buford’s men. Buford holds the Confederates off until infantry General John Reynolds arrives. Reynolds positions his troops and fights the Confederates off, but he is soon killed. Lee arrives in Gettysburg and finds the battle in full fury. Two other Confederate generals arrive and send word to Lee that they have engaged the Union troops, who continue to pour in from the south. Lee orders his generals to attack. Meanwhile, Chamberlain’s regiment begins to move northward toward Gettysburg.

The first day’s battle ends with the Union forces retreating into the hills surrounding Gettysburg. There they dig in, setting up cannons and defensive stone walls. Longstreet is nervous—he knows that the hills are good defensive positions, and he knows that Lee plans to attack them rather than swing the army southeast toward Washington, D.C. Lee meets with his generals and is angry with General Ewell for not following his orders and taking Cemetery Hill and Culp’s Hill, thereby instead allowing the Union forces to retreat into them. Ewell is a cautious general, perhaps too cautious. Meanwhile, Buford returns to the Union camp to discover that he is being blamed for the day’s loss.

On July 2, Chamberlain awakes and his regiment begins moving north again toward Gettysburg. On the way, his regiment discovers an escaped slave, and Chamberlain muses on the reasons behind the war and his thoughts on race. Back at Gettysburg, two of Lee’s generals—Ewell and Early—suggest that the army strike the Union’s two flanks in order to weaken it. Lee likes the plan, but Longstreet still wants to move southeast toward Washington, D.C. Lee refuses, and Longstreet reluctantly agrees to attack the Union’s left flank. As he leads his troops toward the hills to the south of Gettysburg, Little Round Top and Big Round Top, he discovers that the army has come down off the hills and into the peach orchard at the bottom. He decides he has no choice but to attack anyway, and a bloodbath on both sides is the result.

Chamberlain’s regiment finally reaches Gettysburg and is placed on Little Round Top. Chamberlain is told that he is the extreme left of the Union line, which means he can never retreat. Chamberlain and his men hold the hill against numerous Confederate attacks, but eventually they run out of bullets. Chamberlain orders a bayonet charge, and his screaming regiment, charging down the hill, frightens the Confederates into fleeing. The Union still controls Little Round Top at the end of the day, and Longstreet’s men have suffered heavy losses in the peach orchard. That night, Stuart returns, and Lee scolds him for being absent. Lee then decides on a plan for the next day: now that he has battered the two flanks of the Union army, the middle must be weakened. He will charge through the middle of the Union line and split the army in two, then destroy each half individually.

The next morning, July 3, Chamberlain’s men are moved to the center of the Union line, where it is supposed to be safe and quiet. At the Confederate camp, Longstreet tries to convince Lee one last time to swing the army toward Washington, D.C., but Lee again refuses. He is intent on attacking his enemy. Longstreet tells Lee that he is certain Lee’s plan is doomed to failure, but Lee obstinately refuses to budge. Longstreet reluctantly agrees to attack the center of the line and places Pickett in charge of the assault.

The Confederates begin with an artillery barrage in an attempt to weaken the Union artillery on the other side. Chamberlain finds himself and his regiment in the middle of this bombardment, much to his surprise, but he survives intact. Since the Confederate artillery shoots too high, not much damage is dealt to the Union batteries. The Confederate attack begins as the troops start marching across the open field toward the Union troops. The Union begins firing cannons, blowing huge holes in the Confederate line and killing hundreds of men. When the Confederates come within range, the Union soldiers open fire with their guns, killing hundreds more. Pickett loses sixty percent of his division. The Confederates soon retreat, and the Battle of Gettysburg comes to its bloody, spectacular end.