April Morning is the story of Adam Cooper's journey into manhood on the day of the Battle of Lexington during the American Revolutionary War. Adam, a teenager, is struggling on the cusp of adulthood as war looms. He experiences the heady prelude to open combat, but ultimately he is shielded from the battle by family and friends and evades fighting by hiding outside the town. His father, Moses, is killed in the fighting.
The novel begins in the afternoon of April 18, 1775, when Adam Cooper's father, Moses Cooper, sends Adam out to draw water from the well for his mother, Sarah Cooper. After completing this task, Adam heads upstairs to talk with Granny. During the talk with her, they engage in a debate on religion. Afterwords, they head downstairs to eat dinner. Then the family prays and the meal, consisting of bread pudding and donkers, begins. In the middle of the meal, Moses confronts Adam about a "spell" to be said while drawing water. As a result, the confrontation starts an argument, which is interrupted by Cousin Simmons arriving. Cousin Simmons, chosen to draft a letter on the rights of man, comes to Moses with his draft seeking criticism. Another debate arises over Cousin Simmons' description of rights as "god-given." Moses asserts that rights come from the people backing them, not God.
After dinner is over and Adam finishes some evening chores, he heads over to the Simmons' house to meet with Ruth, his love interest, and go on a walk. Before he is able to see Ruth, however, Aunt Simmons makes conversation with Adam and feeds him pie. Then Ruth comes downstairs, and Adam and Ruth leave on a walk. While they are walking, they talk about various things, including their futures and what they want to be in the world. After a kiss Adam walks Ruth home and then he himself heads home. Upon arrival, Adam spots Levi cleaning his gun. Adam does not like this but his mother insists that he let Levi do it. Then Adam heads upstairs and goes to bed. Before falling asleep he overhears his parents talking about the committee meeting. Finally he falls asleep.
Suddenly, Adam is awakened by his brother Levi. Levi draws attention to a speedy rider that stops in the center of town. Now the whole family is awake and curious. People gather around the rider on the green, who informs the town that the British are coming and may be marching through the town. He then rides off. Because of this news, arguments stir in the crowd on whether to muster the militia. The people of Lexington agree to muster it. Adam signs up and is then tasked to take Ruth home. After doing so, he comes to his home to overhear his parents designating him a man. As he walks in his father chastises him, then has Adam load his gun and go to the muster.
After Adam and all the other men arrive at the green, the militia muster falls into order and the women and children are sent inside. They stand there for a few hours until the redcoats march into town. The British fix bayonets, then fire upon the militia. Adam's father falls and Adam runs away. He hides in a smokehouse until Levi comes in. Levi tells Adam to leave the town because the British are searching the town. Adam leaves and jumps over a wall and meets Solomon Chandler. He feeds and comforts Adam on the events Adam just witnessed. Then they walk until they meet Cousin Dover, Cousin Simmons and the Reverend. The company continues to walk until they arrive at the militia encampment. There the militia plans several ambushes and Adam shares his story of the massacre on the Lexington green. Then the militia sends a horseman to scout ahead while the others lie in wait by the road. The horseman returns, then the British come. The militia releases a few volleys before retreating over the hill. The militia, not pursued by the British, stop to rest and plan the next ambush.
During the next ambush Adam falls asleep under some brush. He is awakened by Cousin Simmons and the Reverend searching for his body and talking about him. Adam calls to them, to their relief, and they send him home. He returns home and is greeted by Levi, who walks Adam into the house. The house is occupied by mourners, Ruth, Granny, and his mother. Adam's mother sends him to get his father a coffin and take it to the church. After a brief conversation with the coffin-maker Adam returns home. He eats dinner, then his mother sends him to light candles by his father's coffin. Ruth accompanies him and they talk for a while, until Adam walks Ruth home. Then he himself goes home and retires to bed.