The following version of the book was used to create this study guide: Ireland, Justina, Deathless Divide. HarperCollins, New York, NY, 2020. Kindle AZW file.

Jane McKeene and Katherine Deveraux are two teenage girls who have studied at an elite school to learn how to fight the shamblers. Shamblers are the dead that have risen to plague humanity. Jane and Katherine have already endured hardships and loss. Deathless Divide, the sequel to Death Nation by Justina Ireland, opens just outside Summerland, Kansas. As Jane is running from Summerland, she takes time to look back as shamblers overrun the town. The two girls are part of a small group that escaped Summerland. The others that escaped are the madam of a brothel, a couple of her brothel's girls, an orphaned toddler, Jane's former boyfriend Jackson Keats, and Jackson's younger sister, Lily. Jane and Katherine are planning to go straight to Nicodemus, the town nearest to Summerland where most of the other survivors are headed, but Jackson is urging that they go to Fort Riley. When Jane presses him for a reason, he finally admits that he has gotten married and believes his wife will be there. Jane is heartbroken because she cares for Jackson, even though he has never made any promises. Jackson says he needs someone who will be a mother to Lily and that Jane is prone to run headlong into danger rather than taking care of herself. The group stops for the night and early the next morning, a shambler bites Jackson. He has just enough time to say goodbye to Lily before he begins to turn into a shambler, and Jane is the one he asks to end his life. She is heartbroken again but resolves to hold in her grief until she has the time to cope with it.

The moment they arrive in Nicodemus, Jane is arrested for killing the sheriff of Summerland, but the council quickly acquits her. With a horde of shamblers just outside the gate, scientist Gideon Carr from Summerland wants to vaccinate everyone in town. However, the demand outweighs his supply. Before the horde from outside can breach the wall, Gideon makes a miscalculation that turns several people into shamblers. With shamblers now in the city, there is nothing to do but run. Jane and a group prepare to run, but Jane is bitten. She believes she is dying and urges Katherine to leave. What Jane only later discovers is that she is immune, thanks to Gideon's vaccine. She remains in Nicodemus, among the shamblers, with a girl named Callie who is also immune. Callie realizes that Jane will die of infection unless she amputates her arm.

A year and five months later, Jane and Callie are in California. They are working as bounty hunters, but Jane's true objective is to find Gideon Carr and kill him in retaliation for all the lives Gideon took. Meanwhile, Katherine and a friend named Sue are looking for a place to settle down with Lily. They decide on California. Katherine, Sue, and Lily are traveling with a wagon train when Jane appears, chasing a man she says has a bounty on his head. Katherine is shocked that Jane has become so brutal. Jane seems indifferent to Katherine's presence, but she finds that her hard demeanor cracks. Over the coming weeks, Jane travels with the wagon train but sets out for Sacramento where she believes Gideon has a lab. Katherine has decided she will never again leave Jane's side and face the guilt of knowing she should have saved her friend. They discover that Sacramento has already fallen as the result of more of Gideon's experiments. They catch up with him at an abandoned mining town. Katherine kills him, but not before he injects her with a vaccine.

Katherine and Jane, accompanied by an Indian named Daniel Redfern, arrive in Haven, California, where they reunite with Sue, Lily, and others, including Jane's mother. But Jane quickly realizes that settling down is not what she wants. She decides to set out, believing there is still some good she can do in the world. Daniel accompanies her. As they are leaving, Katherine rushes to Jane's side. The three set out, though without a clear idea of their mission.