Four friends are enjoying their time by the pool at a Cancún resort. Amy (Jena Malone) and her best friend Stacey (Laura Ramsey) are on vacation with their boyfriends Jeff (Jonathan Tucker) and Eric (Shawn Ashmore). Their relaxation is interrupted when Amy discovers that one of her earrings is missing. A boy named Mathias (Joe Anderson) finds it at the bottom of the pool and returns it to her. Grateful for the gesture, Amy and Stacey invite him to join in for a drink. When Mathias mentions that his brother and sister-in-law are excavating an ancient ruin, they eagerly accept his invitation to visit the site, along with his friend Dimitri (Dimitri Baveas).
However, the next morning, the cousins from the dig fail to pick them up as planned. The six friends experience difficulty in finding transportation to the ruins and eventually resort to paying a local truck driver, Patricio Almeida Rodríguez, to take them. As they venture into the jungle, they stumble upon an abandoned truck belonging to Mathias' brother. Although Mathias seems unsettled, they decide to press on and search for the ruins themselves.
They wander deeper into the jungle until they finally appear before a breathtaking ancient structure. However, their awe quickly turns to fear when they are confronted by men brandishing bows and arrows, including an older man (Sergio Calderón) who threatens them with a revolver. Despite Amy's instinctive urge to document the moment with her camera, the situation escalates when Dimitri attempts to surrender the camera as a peace offering and is brutally shot with an arrow, signaling the beginning of a horrific ordeal.
Fleeing to the top of the ruins for safety, Mathias desperately searches for his cousins, while the others realize their phones are useless without a signal. In an eerie turn, they hear a cell phone ringing from a deep shaft nearby and decide to investigate. Mathias, hopeful to find help, is lowered down the shaft by the others but falls when the rope snaps, leaving him severely injured. Stacey bravely volunteers to retrieve him, but ends up injuring herself in the process.
As tensions rise, the group debates their options while trying to take care of Mathias. In an act of frustration, Amy confronts their captors and inadvertently puts them all in further jeopardy when their presence leads to an escalation in violence. Shocking events unfold, including the shocking death of a young boy at the hands of the captors. When the friends realize their predicament has grown dire, they attempt to seek refuge, but the morning brings harrowing results as Stacey awakens to discover a vine growing into her leg from her previous injury.
Desperate to rid themselves of the vines that seem to be taking over, the friends engage in a series of traumatic events involving surgery and horrifying discoveries about the sentient plant that surrounds them. As the group's situation becomes increasingly dire, with friends falling victim to the plant's sinister grasp in one harrowing moment after another, trust begins to erode, leading to accusations and chaos among them.
Ultimately, they are forced to confront an insidious reality that threatens to claim them all. Jeff devises a plan of escape, sacrificing himself to protect Amy, who manages to flee the chaos in a Jeep. As she speeds away into the unknown, the sinister presence of the vines and the dark fate of the others linger ominously. In the aftermath of their harrowing ordeal, Dimitri's friends arrive, unknowingly stepping into the path of a historical horror.
