The Key Within
Macallan activates the communications device secretly given to her by Anton and Othello. They immediately rush to her aid and rescue her and Tulley from freezing to death in the Gulf of Alaska. During the flight, Macallan examines the sarcophagus, which represents the supposed Key that the immortals have been searching for. The sarcophagus opens to reveal a cavity inside into which Macallan climbs. Once inside, she finds her body transformed as her recessed immortal genes become activated and she becomes a full-fledged member of Leviathan. She becomes immortal!
But soon it becomes clear. The sarcophagus was not the real "Key". Macallan, being transformed into her full potential, was. And now with her genetic destiny fulfilled, she must learn to what higher purpose she is being called to answer.