En route to San Diego, a pregnant woman named Becky and her brother Cal stop after hearing cries for help from Tobin, a young boy accompanied by his mother Natalie in the tall grass. Concerned, the siblings enter but get separated and find that their distance changes unnaturally. They decide to leave but cannot find the road. Becky encounters Tobin's father Ross, who tells her to stay close and not to lose sight of him, but she does so. Cal stumbles across Tobin, holding a dead crow. Tobin claims that the grass will not move dead things and buries the bird in the path, saying that a rock mentioned that Becky would die soon. When Tobin leads Cal to a rock in the field and tells him to touch it, he hears Becky's scream before a ghost attacks him. The father of Becky's unborn child, Travis, arrives looking for the siblings. He investigates the field, stumbling across Tobin, who implies that they know each other and leads him to Becky's corpse, saying that the field does not move dead things. Tobin arrives at a nearby church with his parents. He and Freddy, the family dog, hear Travis shouting Tobin's name from the grass. Freddy is drawn in, which leads Tobin, Natalie, and Ross to follow and get separated. With the family panicking, the siblings re-enter the grass as Tobin states that Freddy died. Travis, Becky, and Cal move toward Tobin, and all four find each other. Travis says that the siblings have been missing for two months. Later, the group spots a building in the distance. Becky receives a call from someone warning them not to keep making the same "mistake". The grass seemingly enters Becky's uterus, and she passes out, only to be revived by Ross, who then reunites with Tobin and says that he will show them out. Ross leads them to the rock, where Natalie confronts them. She warns them not to touch the rock, and that Ross is dangerous, telling the others to leave. Travis attacks Ross who then dislocates his arm and crushes Natalie's head. Ross claims that the rock showed him the truth and the way out, but he does not want to leave. Becky, Cal, Travis, and Tobin reach the building. It is revealed that Travis originally was not interested in being a father and asked Becky to abort their baby, which she refused. As a result, the siblings traveled to San Diego to meet a family interested in adopting her baby, as she did not feel ready to be a single parent. Travis expresses regret and now wants to be part of his child and Becky's lives. While scouting, Travis and Cal discover that Freddy has escaped the field via a "hole" that leads to the road. Cal lets go of Travis as he slips, causing him to fall off the roof. Tobin flees into the field when Ross follows them to the roof. The two follow Tobin, but Becky refuses to leave Travis and goes back as Cal flees. Ross strangles Cal to death. They are in a
time loop, with Cal permanently being hunted by an insane, possessed Ross in the grass. Travis survives and searches for Becky. Ross attacks Becky, who escapes. A thunderstorm begins. Grass Creatures confront and carry Becky to the rock, which has
prophetic marks relating to her pregnancy. Becky makes a phone call, pleading for her past self to prevent Cal from hurting Travis. As she screams in pain from contractions, the ground underneath the rock opens, revealing roots that turn into
humanoid figures reaching toward her. She passes out and wakes up to Cal. He is holding her baby. She falls asleep again and wakes up to Cal feeding her baby to her and saying that it is just grass and seeds. Becky realizes that "Cal" is Ross. Tobin finds Travis and says that Ross killed both the baby and Cal, and will keep killing them repeatedly. They are confronted by Ross, who mortally wounds Travis. As Ross attempts to force Tobin to touch the rock, Becky attacks him before dying from her wounds. Travis strangles Ross with bundled up grass. To understand, Travis touches the rock and has visions. Travis grabs Tobin's hand, guides him to an exit, states that he is not leaving and instructs Tobin to stop the siblings from entering. Tobin emerges across the road as the siblings are about to enter the grass, convincing them to stay out by showing them Becky's necklace that Travis gave him, closing the loop. Becky decides to keep her baby as they drive back home. Travis listens to them leaving and then dies. ==Cast==