swims over, but as he approaches, Nicolai is dragged underwater by one of the creatures. Jack lights a flare and swims deep below the surface, where he can see the creature pulling Nicolai to his death. However, Jack clearly sees tattooed letters on the creature's hands, proving the mutants were once human. Jack regroups with the team on shore. But his senses and physical features are beginning to transform as a result of the scratches he got earlier. His hearing has improved significantly and his other senses are heightened. When Jack tells them they must go back up the cave wall to escape, Charlie scales the wall but is soon attacked by a creature hidden in the passage above. The human-sized winged mutation kills her on the cliff face in full view of the team. As Jack exhibits super-keen senses and inhumanly slanted pupils, Kathryn theorises that what is happening to Jack has happened before. She speculates that Jack, the previous explorers and all the ecosystem's creatures mutated due to the parasite; the infected humans now resemble the winged demons depicted in the mosaics. Witnessing Jack's transformation, some of the survivors question his judgement and the team splits up. Alex, Briggs and Kathryn go their own way, while Top and Tyler stay with Jack. Jack, Top and Tyler discover a cavern littered with human skeletons and realize this is the ancient battleground depicted in the mosaics; the abbey's residents battled these creatures centuries ago and sealed the cave to prevent them from escaping. Jack notices there is light and cold water coming through the center of the river, which confirms this is the passageway out of the cave. He lets Tyler go back to find the others, but in doing so he witnesses Briggs's death - impaled on spikes on the cave wall. Tyler saves Kathryn and brings her to the passageway. On their way back, they meet Alex and all run to rejoin Jack and Top. However, the creatures have entered the cavern and stolen the rebreathers necessary to navigate the passage. Top, Kathryn, Tyler and Alex run into the river toward the passageway, but Alex is killed before he can get in the water, a creature grabbing him from above. Jack causes a distraction, allowing the others to escape while he sacrifices himself by battling the creatures. The three resurface in a huge canyon and are finally safe.