The story starts with Nick and Lori, a newlywed couple who, after eloping, want to take a mule ride down into the canyon with a guide, Henry. The next day the trio head down into the canyon. After traveling for a while the guide offers to take them to old petroglyph, which are a half day's ride away. After some convincing from Nick, Lori eventually agrees to the journey. Along the way, Henry is bitten twice by rattlesnakes and in the process the trio's mules flee. They are forced to make camp and begin heading back the next day. The guide is delirious and later in the day succumbs to the venom and dies. The couple bury him and are left to struggle on to find a way out. After a day's hike, the couple eventually reach a dead end where the petroglyphs are. Realizing they have spent the last day going the wrong way, they decide to attempt to climb up the rock face in the hope of getting a signal on Lori's phone. Lori manages to call the emergency services but has only time to say they are in trouble before losing signal. Nick loses his grip in the crevice and the couple fall, breaking Lori's phone and Nick's leg, which gets trapped in a crevice at the base of the rock face.