A year after a tragic accident claims the life of her husband and daughter, Sarah, along with five of her friends, ventures into a remote cave system in the Appalachian Mountains, seeking adventure and solace. The group, led by the fiercely independent Juno, consists of thrill-seekers who have previously shared adrenaline-pumping experiences together. As they embark on their journey, they're faced with the physical challenges of spelunking—the climbing, crawling, and swimming through narrow passages and underwater pools—all while attempting to strengthen their bonds and support Sarah in her quest for healing.

However, their adventure takes a dire turn when a cave-in blocks their return path, trapping them inside the unknown and uncharted system. Panic and claustrophobia set in as they frantically search for another way out, realizing they must delve deeper into the cave's depths to survive. The situation escalates when they come across ancient paintings that suggest the existence of an undiscovered entrance or exit. As tensions rise, the group's camaraderie is tested, revealing fractures in their relationships. Meanwhile, they start to perceive strange noises and movements in the darkness, hinting that they might not be alone in the cavernous depths. Unbeknownst to them, the true horror of their situation has only just begun to unfold, as they face not only the psychological and physical demands of their entrapment but also the realization that they may have intruded into a realm where they are not welcome.