Hopper, an archaeology professor, is exploring a remote cave system on the trail of missing hippies from the 1970s. After discovering what appears to be a cowboy paused in place in a tunnel, he returns to town and dismisses his graduate students, Taylor and Jackie, stating that their research is done. Several days later, Hopper has not returned, and Taylor is worried about his safety. Taylor and Jackie decide to look for him, along with their friend Cara, who is watching her sister, Veeves, and her sister's best friend Furby. They follow Hopper's trail to the campsite near the cave, finding an entrance with climbing ropes leading inside. They decide to follow it, but Furby chooses to stay behind as backup for the base camp. The group lowers themselves into the cave system and encounters strange noises. When Furby does not answer their radio calls, Jackie tries to climb back out, but her rope frays, and she falls, injuring herself and Taylor. Calling for help, they receive a transmission from inside the cave and follow it. At a different junction, they discover an overhead opening to the cave and Furby, dead with a broken neck. In watching his video recordings, they notice that several days elapsed from his perspective, while only about an hour had lapsed in the cave. His recordings show that he began researching the hippies' belongings, discovering that they were actually Hopper's parents and that Hopper is searching for his missing sister. His parents were following legends of the Fountain of Youth and speculated that this cave system was the root of the myth. After several days, Furby descended into the cave to retrieve keys for a vehicle but fell when his rope severed. Taylor theorizes that the cave is inside a time distortion where events move more slowly. With few options, Cara free-climbs out of the cave in order to get a GPS signal. Outside, the terrain has become barren, and she cannot get a signal. After returning to the cave, her companions compare video recordings, confirming Taylor's theory. They then review Furby's footage once again and learn that he survived the fall only to be murdered by a caveman. Cara and Taylor deduce that the time difference is much more drastic than they suspected and that entire years are passing within seconds, meaning the few hours they have been in the cave is enough to span several hundred or thousand years outside. Hearing more howling, Cara prepares to climb out again in search of help but is interrupted by a futuristic humanoid spaceman descending via a retractable ladder. A caveman suddenly attacks, but the spaceman subdues him non-lethally. The group flees just to find a whole tribe of cavemen inspecting the dead bodies of the cowboy and Hopper's parents. Discovered, Taylor fights the cavemen and is killed in the process. The spaceman returns, protects the others from the cavemen, and then places Taylor into the pool of water, which heals him. More cavemen attack, and the spaceman is fatally wounded, but he uses his dying breaths to show the group a series of media clips, explaining their disappearance and indicating that humans have become a spacefaring race. Taylor finds Hopper injured in front of another time dilation, containing Hopper's long-missing sister along with a legion of conquistadors in battle with the aborigines for the control of a waterfall at the center of the cave system. Hopper explains that the field is strongest here, making rescue of his sister impossible from within the melee; he tells Taylor to go and save the others, as he is also dying. The group prepares to leave the cave, using the spaceman's ladder through the overhead opening. However, the cavemen attack before they can get through; Cara is pulled through the portal by grey-clawed beings before she can help her friends. From their perspective, she reappears through the portal, differently dressed and accompanying rope-like mechanisms which pull her friends through. A short time later, Furby awakens, revived along with Hopper and his family, having been retrieved from the cave. The others arrive, happily explaining that they are in the far future in a space station and have a lot to talk about.
The film was initially conceived as found footage. Shooting took place in Texas. Co-director Mark Dennis cited 1980s films, such as the Indiana Jones films and The Goonies, as an inspiration, in particular those films' focus on practical effects, characters, and plot. Setting the film in a cave came from both growing up in Texas, where caves are plentiful, and from The Descent. The premise came from a long, cross-country trip that Dennis took. When he returned to the United States several years later after having been out of touch with his friends, he was surprised by how much had changed.
Based on 10 reviews, the film holds a 60% approval rating on Rotten Tomatoes. On Metacritic, the film scored 46 points out of 100, based on four critic reviews, which indicates "mixed or average reviews". Gary Goldstein of the Los Angeles Times described the film as "a handful of intriguing ideas in search of a more cohesive and dimensional narrative". Though labeling it a good film, Roman Morales of Ain't It Cool News wrote that the film's pacing and excessive exposition keep it from being great. Danielle White of the Austin Chronicle gave the film one and half stars out of five, commenting, "If anything, there’s wasted potential with the plot and story development. And, of course, some logistical points that don’t make sense. But it’s also really short. Most films that traffic in such heady subjects are, like, three hours long. An anxiety-ridden contemplation on history and mortality simply needs more time."
