The world has been overrun with Unconsecrated (flesh-eating zombies). Mary lives in the middle of a forest, in a small village protected by fences. One day she hears sirens alerting the village that there may be a breach in the fences.
Mary discovers that her mother has been infected, and dies. Her brother Jed bans Mary from their house. Mary then joins the Sisterhood of nuns after Sister Tabitha threatens her. During her stay in the Cathedral, Mary meets Travis, a wounded citizen as well as her childhood friend, and tells him her mothers stories about the ocean.
One night, a young girl named Gabrielle wanders into Mary's village. She is brought into the Cathedral, where the Sisterhood keeps her locked up. Mary gets a chance talks to Gabrielle through the walls of her room, but the next night Gabrielle's room is empty. Mary later finds out that the Sisterhood forced her into the forest, where she was bitten by a zombie and turned into one herself.
To help her escape the Sisterhood, Harry proposes to Mary, who accepts, even though she's in love with his brother, Travis. On her wedding day, sirens go off again, but this time the unconsecrated have breached the fences. Mary, Travis, Harry, her best friend Cass, a young boy named Jacob, her brother, and his wife escape by entering the forest. They explore the forest by using a labyrinth of fences and find an abandoned village. After a few minutes of exploring, they find out that the village is crawling with unconsecrated. Mary and Travis run to a house, as Travis is unable to climb the ladders that would bring them to the safety of the tree houses, where their friends have escaped to. Mary and Travis spend a lot of time together and fall in love.
The zombies eventually break into their house, but Mary and Travis manage to escape. They make their way into a tree house, where the rest of the group is staying. Jacob starts a fire in the village, and Travis gets bitten by a zombie in the process of trying to escape. Mary ends up cutting off his head in order to save him from being a zombie.
As they continue walking through the fenced path in the forest, Mary decides to leave her friends and find the ocean. She finds a gate and runs into the forest, where she is quickly outnumbered by zombies. Jed dies in the process of saving her. She arrives at the edge of a cliff and jumps off into a river in an attempt to escape the unconsecrated. A man finds her washed up on shore and brings her to his home, a lighthouse.
