Angie and Andy are two twenty-somethings who decide to run off together, away from their little hometown in Pennsylvania. They head for the West, acting like a married couple despite only having known each other for a couple of days, ready to experience magic out in the sun. They have little money, their prospects for endurance are few, and their dreams are already diverging, but youthful insistence overwhelms them both. They can't see anything clearly. After a couple days of driving, they reach Joshua Tree. A park ranger tells them about how the Joshua trees may soon be extinct, which would knock out the codependent yucca moths that feed on the trees. However, it's too soon to tell whether the Joshua trees will really disappear or not. During their hike, Angie pricks her finger on the dagger-like limbs of a Joshua tree. Her system is never the same again: her mind is taken over by the spirit of the tree that wounded her. She begins acting strangely. Her eyes change colors, she no longer seems interested in her road trip with Andy and tries pushing him away, and all she longs for is to be in the desert. Irritated and confused by Angie's sudden change of heart, but now tied to her in a way he doesn't understand, Andy decides to stay with Angie, despite her protestations. They take up a room in a hotel for an extended period of time. During that time, Angie is largely inaccessible, but Andy learns how to navigate her various moods. Andy continues to think about going, but every time he makes up his mind to leave, he's pulled back in. Eventually, they sign a lease on a house with three Joshua trees in the backyard. Meanwhile, the spirit of the tree wars with Angie's spirits. During the spring, it's dormant, due to its leaves having fallen off, and she has more clarity and remembers those moments with Andy before she was possessed. At other times, she's volatile and flocks to places and images that remind her of the freedom of the desert: church, flower-patterned wallpaper, an abandoned jacuzzi. On their anniversary, Andy invites Angie out to go dancing. For once, Andy, Angie, and the tree are in perfect harmony: all three enjoy the ritual of dancing. Andy prompts Angie to reminisce, which the tree fights back against–nostalgia would push it out of her vessel. Speaking through Angie, the tree suggests visiting Joshua Tree again. Angie and Andy make their way over there, and mid-sex, the tree compels Angie to steal Andy's knife. Right before it can kill him, Andy reminds Angie of the beginning of their journey, that night they met each other in Pennsylvania. The memory pushes the tree back; Angie returns to her old self. On their way out of the park, Angie and Andy see the ranger they met about a year ago. Annoyed, Andy decides he'll wait in the car. Angie stays and asks him questions about the survival of the Joshua trees. The ranger says that, even if the trees look as though they might be dying now, he wouldn't be surprised to see them come back to life soon.