On the road to San Diego, Cal and his sister Becky discuss the fact they’re running away
from home because Becky is six months pregnant and their parents didn’t take it well. Becky is
second-guessing their decision when she suddenly begins feeling sick, so Cal pulls over near a
church to let her throw up. When they’re about to leave, Becky says she hears the voice of a
boy screaming for help in the tall grass. Cal decides to park the car by the church and the
siblings talk back, learning that the boy has been stuck in the grass for days. At that moment,
a book is seen on the side of the road and the voice of a woman is also heard in the grass
telling the boy to stop shouting. Judging by the volume of the voice, Cal assumes the boy is near
the road and decides to go into the grass to help. Becky follows him while she tries to call 911,
but then she loses reception as she goes deeper. When she puts her phone down, Becky realizes she
lost Cal in the grass. She begins speaking loudly to locate her brother and suggests they head back
to the car because something doesn’t seem right. First they need to reunite, so Becky
loudly recites an old naughty rhyme, but this makes Cal confused: at first her voice is coming
from his right then suddenly her voice is coming from his left. Next they agree to jump to figure
out each other’s location. On the first jump they see each other but on the second jump they
suddenly much farther away even if they didn’t walk. After the jump, Becky falls into the mud,
and a panicking Cal decides to run toward her to help. Now it’s Cal who falls into the mud and he’s
shocked to find a dead dog named Freddy with flies hovering all over him, apparently he’s been here
for a while. Hours pass with the siblings unable to find each other or the exit, and as the sun
goes down, they accept they’re stuck in the grass field. Becky tries calling her brother again,
but she gets really tired so she sits to wait for Cal to find her first. Suddenly a creepy figure
appears among the grass, but it turns out to be just a man named Ross, who offers his help to take
her out of the field. He explains he's found a way out but hasn’t left yet because he is looking for
his wife and son, whose voice the siblings heard early. Becky is wary of him, but she has no other
choice but to accept his help, so they go looking for Cal together. Some more time passes, and Cal
keeps calling for Becky to no avail. As he sits there disappointed, something suddenly startles
him: it’s Tobin, the boy that had been calling for help earlier. He consoles Cal and says it's easier
to find things once they’re dead. Weirded out, Cal asks if Tobin was the one who lured them into the
field, but Tobin says he and his family went in because they heard a man calling for help too and
he has no idea how long they’ve been here for. Tobin says that his sister will be dead soon,
and Cal wonders how the boy knows Becky is his sister, Tobin replies that the rock told him the
truth. Apparently it’s the rock that teaches you how to hear the grass and that’s how you
get to know about things. Then Tobin beings guiding Cal to Becky. Meanwhile Ross and Becky
talk about her baby, and Ross guesses that the father of the baby isn’t with her. As they walk,
Becky finds medicine bottles and scissors on the ground, not understanding how they got there. When
she looks again, she discovers Ross isn’t there anymore. She begins calling for him to no avail,
so she changes to calling Cal. As she looks around for any signs, something suddenly grabs
her and takes her into the grass. Back to Tobin, he takes Cal to a small area with no grass with a
mysterious giant rock in the middle of it. Tobin urges Cal to touch it, but when Cal comes closer,
he hears whispers of what seem to be tribal chants. Right before Cal touches it, Becky is
heard screaming, and Cal immediately runs in the direction of her voice, ignoring Tobin warning
him to not get in there. Suddenly the day changes to a clear day; showing a truck stopping at a gas
station on the same road as the church. This is Becky’s ex Travis, who has come to look for the
siblings. Since he finds nothing at the train station, Travis continues his journey and finds
Becky and Cal’s car parked by the church. When he looks inside the car, he sees bugs and dust,
indicating the vehicle has been there for weeks. Travis begins calling their names and looking for
them, but there's no response. Next he enters the church, but it’s empty too. On his way out,
he sees a book on the ground and picks it up only to see Becky’s name on it. Suspecting the
siblings entered the grass field, Travis goes in as well, folding the grass and following the sun
so he can keep track of how to get back. Unfortunately every time he takes a step,
the grass just unfolds itself. After a few steps, Travis realizes the sun isn’t in the correct
spot anymore, but regardless of his confusion he keeps moving until night falls. Since he’s tired,
he stops to lie on the ground and stare at Becky’s photo. Suddenly something startles Travis:
it’s Tobin popping out of nowhere. As whispers and laughter can be heard in the tall grass,
Tobin reveals he knows Travis’ name and that he's looking for Becky, saying he can take him to her.
Travis doesn’t hesitate to follow him, only to be incredibly upset to discover Becky’s dead
body right in the middle of the field. As Travis clings to her crying, Tobin explains the grass
doesn’t move dead things because it makes them easier to find. When Travis looks up,
Tobin is gone. The next morning, Travis wakes up and sees Becky’s dead body right beside him.
He picks up a necklace from her body and starts moving again, but then he hears someone and starts
calling for help. It’s Tobin who responds back, and Travis calls for him again so the boy can find
him. However the Tobin that shows up looks clean and healthy, and he’s there with his mom Natalie,
his dad Ross, and the dog Freddy. This reveals that the grass field is stuck in some sort of
time loop. Suddenly Freddy runs into the field and Tobin follows him, ignoring Natalie’s warnings. At
that moment Travis realizes Tobin has managed to leave the field and tries to tell him not
to come back inside, but it’s too late, the boy is coming for his family. Natalie thinks
she hears Tobin nearby and splits up from the group to find him. By the time night falls,
Ross is looking for his family alone and comes across the mysterious rock. The next morning,
Tobin is shouting for help while Becky and Cal are outside the field with the car again. However
this time Travis is in the field too. When he hears Becky’s voice, he calls her name, and both
siblings are shocked to hear him before replying. Travis tells them that he came looking for them,
which Becky finds hard to believe. Suddenly they hear Tobin’s voice reciting Becky’s rhyme, and
Travis follows it to finally find the boy. Becky does the same thing and is reunited with Travis,
making the moment rather awkward. Shortly after, Cal shows up too and he clearly doesn’t like the
fact Travis is there. At that moment, the group finds Freddy’s body. To add to the confusion,
Travis tells the siblings that they’ve been missing for two months, but they don’t believe
him because from their perspective, they only left two days ago. Suddenly Becky feels like someone is
watching them and says they need to go, so Travis picks up Tobin on his shoulders for the boy to
find a way out. Fortunately he spots a building in the distance, and they start walking toward
it. Cal asks Travis if he told anyone about them, hoping that someone will come looking for them,
but sadly Travis didn't tell anybody. At that moment, Becky feels some pain in her belly,
prompting Travis to ask about the baby. Becky tells him that it’s a girl and lets him touch
the belly to feel the baby move. Suddenly, a phone rings and they’re shocked to receive a call from a
voice like Becky’s, who is crying as she asks them to not let Cal hurt Travis because they will keep
making the same mistake again and again. It all seems unbelievable and the group decides to keep
moving, unaware that someone watches them through the grass. A few steps later, Becky slips in the
mud and as she falls, she sees mysterious visions of a baby, tall grass, and strange
people coming toward her, which terrify her and makes her faint. Cal and Travis run toward her,
but at that moment Ross shows up and tries to help her too, saying he can lead them out. Travis tells
him about the building they saw and lifts Tobin again, but this time he can’t see the building,
it’s only grass everywhere. Ross mysteriously says that’s how things work in there. The group keeps
walking and eventually they reach the rock again. This time they notice there are carvings all over
the rock, and somehow Ross knows it refers to a higher knowledge, which he explains as he touches
it. Everyone thinks Rossi is being creepy and he urges Cal to touch the rock too, saying he’ll
also receive knowledge. Before this can happen, Natalie comes out of the grass and stops him,
telling her own husband to stay away from them. She’s obviously terrified of him and tells the
others that Ross is lying before explaining that she had seen Becky and Ross before, but Becky
wasn’t alive and Ross tried to hurt Natalie. Ross denies this and while they argue, Becky sees the
visions again, but this time she also sees Ross in the grass looking very supernatural. Terrified,
Becky tells Travis and Cal they should leave. They try to get Natalie and Tobin to go with them, but
Ross is still trying to manipulate them to touch the rock. Travis cuts it, triggering an argument
that soon becomes a physical fight. As the men exchange blows, Becky asks Cal to help Travis,
but Cal refuses. While they fight, Ross keeps insisting that Travis should touch the rock and
finally overpowers him to win the fight. Next Ross attacks Natalie, showing he’s truly lost it when
he smashes her head with his bare hands. The rest of the group runs away from Ross and finds Freddy,
so they begin to follow him until they reach an abandoned building. Once they get inside, Travis
and Cal blame each other for this mess, starting an argument. Cal blames Travis for abandoning
Becky, accusing him of wanting Becky to terminate the baby, and Travis retaliates by saying Cal has
naughty feelings for his sister, causing Cal to throw a punch and start to fight. At that moment,
Ross catches up and tries to break the door. The group immediately takes the stairs to the roof and
looks around the area, where they see the church across the field. Unfortunately they would have
to go through the grass to reach it, so they try to figure out another plan. Suddenly Travis sees
Freddy running by, but the dog disappears when he walks into the grass. This makes them think there
is a hole in the loop that can lead them out. Trying to look for more clues, Travis has a closer
look at the field by standing on the edge of the roof, which causes him to slip. Cal notices,
but he does nothing to save him and Travis falls to the ground. All this is seen by Tobin and when
Cal notices the boy, he tries to explain himself. However at that moment Ross begins getting closer.
The group runs again, but Becky asks about Travis, refusing to leave without him. When
Cal can’t provide an answer, Becky gets suspicious that he did something to Travis and she walks away
from her brother. Cal tries to follow her but Ross suddenly catches him, revealing he knows
the truth about the Travis incident. Cal tries to escape but Ross doesn’t let him go and holds him
to the ground as he struggles for his life. At that moment, many bodies appear in the field of
grass. Travis turns out to be alive, and he gets up to look for Becky again. He yells for her name
and she answers, but they can’t see each other. Giving up, they both lie in the grass and talk
about their child again, so Travis says he’s happy Becky’s decision to keep the baby. However Becky
confesses that she wasn’t going to keep the child and that’s why they were going to San Diego, there
was a family there who wanted the kid. Upset, Travis swears he will find a way out. Suddenly
Ross shows up and attacks Becky. In the struggle, Becky manages to grab the scissors that she found
on the ground, but Ross quickly disarms her. Then he brings her down to the dirt, intending to take
advantage of her, but this gives Becky the chance to grab the scissors again and stab Ross in the
eye. As it starts to rain, Becky runs as fast as possible, only to freak out when she notices there
are dozens of grass people coming to her from all sides. These weirdos grab her and pull her
into the grass. Moments later, Becky finds herself lying in the mud in front of the rock. She pulls
her phone out and makes a call, which turns out to be the one they heard earlier about not letting
Cal hurt Travis. Suddenly the grass people come back and surround Becky as she screams in pain
because her body has decided to deliver the baby. The visions come again and this birth matches the
drawings on the rock. After lots of pushing, Becky hears the baby crying, but she can’t see
her. Suddenly the ground shakes and opens into a giant ditch between the rock and her. Becky stands
on the edge and looks inside, where she sees many people clinging to the branches of an old
tree while trying to come out. Becky screams and moves back before exhaustion takes over her and
she passes out. Moments later she opens her eyes and asks about the baby. Shockingly it’s Cal who
answers as he calms her down and gives her some water. He also holds a baby and shows it to her,
making Becky relieved. As she closes her eyes again, Cal begins feeding her, and Becky is so
hungry she takes it all. Cal says it’s grass and seeds, but Becky thinks it tastes like something
else, and she freaks out when she realizes she’s eating human flesh and that Cal is actually Ross.
Meanwhile Travis is badly injured yet he keeps searching for Becky. Eventually he finds her alone
on the ground, and when Becky asks about the baby, Travis touches her belly and realizes the baby is
gone. As he cries in grief, Tobin reappears and tells him that Ross killed everyone. He
also explains Ross is never going to stop and that he will kill them over and over again. A
terrified Tobin starts to cry, so Travis hugs him and says he won’t let anybody hurt him. Afterward,
Travis shouts and asks Ross if he wants to kill him. Ross immediately appears from the grass and
attacks Travis, trying to kill him while ignoring Tobin’s pleas to stop. Ross attacks Travis with a
bone and makes him fall defeated before going after his son. Tobin tries to run, but Ross
catches him and tries to force him to touch the rock. Suddenly Becky gets up and hits Ross from
the back, causing him to drop Tobin as Becky falls again. At that moment Travis stands up too and
attacks Ross, hitting his head against the rock and finally killing him by tying some grass around
his neck. Then Travis goes to Becky and holds her as he cries. Not knowing what else to do,
Travis approaches the rock as Tobin warns him that if he touches it he wouldn’t be able to leave.
Travis ignores him and touches it anyway, which makes him feel weird. Suddenly a red light emerges
from the rock and spreads all across the field, almost as if cleansing the area. Travis now looks
creepy like Ross used to, making Tobin afraid. The boy starts to run away, but Travis stops him,
asking him to come with him. Ross hadn’t been lying, the rock did give Travis knowledge of
the grass field. He takes Tobin near the entrance and asks him to go out to warn Becky and Cal so
they won’t come inside the field again, hopefully this will destroy the loop. Then he gives Tobin
Becky’s necklace and pushes him out of the field. In the blink of an eye, Tobin appears in the attic
of the church. He opens the door and makes his way outside, where he sees Becky and Cal’s car
standing on the road. They are about to enter the field because they heard someone calling for help,
but Tobin runs to them and stops them. It looks pretty weird because it’s his own voice that
comes from the grass as well, and a confused Cal begins approaching the grass. Tobin keeps
begging to Becky to stop him and to prove his story, he reveals the necklace Travis gave him.
Becky is shocked as she compares it to her own necklace, and when Tobin mentions Travis’ name,
it’s finally enough for Becky to go to stop her brother. Afterward, Becky convinces Cal to leave,
and they take Tobin in the car with them. However instead of going to San Diego,
Becky asks him to go back because she’s decided to keep the baby. In the field, Travis hears
Becky’s words and is happy with this change, so he lays down and lets the grass cover him.