Dr. Jason Cole is a highly respected neurosurgeon who has it all - a lucrative career, confident charm, and the gift of compassion. But he also has a deep, dark secret. One morning, when he wakes up disoriented in a wrecked hotel room amidst several near-naked women he's never seen before, he knows one thing: it's happening again. Every night at the same hour, something inside Jason changes, leaving him almost unrecognizable - seductive, devious, borderline sociopathic. This new man is his dangerous alternate personality who goes by the name of "Ian Price.

Jason's attempt to control Ian's spending backfires when the doctor comes to in a random sports car tailed by a drug dealer. Meanwhile, a falling out between Jason and Lena prompts a late-night visit from Ian; Dr. Jordan tries to get to the bottom of Jason's behavior; and Olivia worries about her son's new imaginary friend.

Ian breaks an important rule by beating up a man in a bar brawl, which puts Jason's medical skills to the test. Meanwhile, Jason tries to mend his relationship with Lena; and Olivia is unnerved by Ian's stalking.

Jason makes a deal with Ian that he can see Olivia, but only on the condition that Ian pose as Jason at a formal affair to honor Dr. Young, though the evening is nearly ruined by Ian's behavior, which pushes Lena away and puts Young's daughter in danger. Later, Olivia meets Ian in a hotel room, but it's a rendezvous he may soon regret.

Ian has a new love interest whom he met in D.I.D. therapy, but Jason worries about her health, and when he tries to help her it might mean the end of Ian's romance. Meanwhile, Dr. Jordan tells Dr. Young that someone altered her daughter's chart; and Lena pursues a new relationship.