Becoming follows Alex (Toby Kebbell) and Lisa (Penelope Mitchell), a couple newly engaged and deeply in love. While on a road trip, they encounter an ancient evil force that chooses Alex as its new host and begins to slowly take over his mind and body, gradually transforming him into someone terrifying and violent. The changes are small at first. His handwriting. His body language. As Alex struggles with the horror of losing his identity, Lisa notices the shifts in the man she thought she loved. Is he falling out of love with her, or is it something far, far worse? Lisa tracks down Kevin (Jason Patric), a damaged survivor of the entity who has dedicated his life to defeating it. Together, they must outwit an indestructible malevolence that doesn't want to destroy Alex, it wants to be him.