A leisurely Mexican holiday takes a turn for the worse when a group of friends and a fellow tourist embark on a remote archaeological dig in the jungle, where something evil lives among the ruins.
In a brief prologue, a woman crouches alone in darkness, and screams for help before she is dragged by an unseen force. Two young American couples — Jeff, Amy, Eric, and Stacy go on vacation to Mexico. They meet Mathias, a German tourist, who is looking for his brother Heinrich. His last known location is an archaeological dig at a remote Mayan ruin in the jungle. They are also joined by Dimitri, Mathias' friend. The group reaches the ruins of a Mayan temple, and are confronted by Mayan villagers armed with knives, bows, arrows, and a gun. Mathias tries to explain their purpose, but the villagers do not understand Spanish or English. When Amy accidentally steps on some vines, the villagers become extremely agitated. Dimitri approaches the villagers, hoping to appease them, but they shoot and kill him. The rest of the group flees up the steps of the ruins.
At the top, they find an abandoned camp and a shaft in the center. They hear a phone ringing from somewhere inside the ruins. The group lowers Mathias down the shaft with a rope, but it breaks and Mathias falls, becoming paralyzed. Amy and Jeff descend the temple steps hoping to reason with the Mayans, but to no success. In anger, Amy throws a clump of vines which hit a young boy, whom the Mayans promptly kill. They realize the Mayans are afraid of the vines, and will not let them leave as they have all touched them. Later, Stacy and Amy descend the shaft to rescue Mathias.
The next morning, Stacy sees a tendril of vine has crept into a wound on her leg. The vines have also wrapped themselves around Mathias' lower legs and eaten them down to the bone. Eric and Jeff are barely able to remove the vines from Stacy, but cannot get them off of Mathias. The phone is heard again from deep in the shaft so Stacy and Amy descend again. In a small, vine-covered room, the two find the body of the young archaeologist, Heinrich's friend, and a broken phone. They then realize that the ringing sound was made by the flowers of the vine. As Amy touches one flower, the vines attack and the two barely escape.