In the bad ending, where Claire defeated Neil and thus Moira never overcame her fear of guns, Alex is immediatly successful. Awakening in Natalia's body, she destroys her own former, mutated body and reveals herself to Barry, leaving him to die on the island.
In the good ending, Moira arrives in time to save Natalia, distracting and temporarily repelling Alex with gunshots. Barry, Moira and Natalia escape the area, but Alex, mutating even further, gives chase and ultimately corners them on the edge of a cliff. Claire arrives in a helicopter to rescue the trio, and their combined efforts take Alex down. As they leave the island, Barry expresses his intention to retire and raise Natalia, who remained strangely quiet, as his daughter. In an epilogue, Claire is informed that her brother is in China and tells Piers to take good care of him. She heads towards Barry's home, where Natalia, surrounded by newspapers reporting on bioterrorism, finishes reading The Metamorphosis by Franz Kafka and smiles ominously, revealing Alex succeeded, to some extent, in taking over her body.