After a late-night car accident involving the increasingly self-destructive Kovac and med student Harkins, the hour unfolds backwards to recount the troubling events leading up to the crash. A boozy holiday party, rumors of an illicit tryst and a run-in with his ex, Abby, all plague Kovac, but it's his tragic misdiagnosis of a patient that ultimately sends him racing off on a reckless ride. Meanwhile, the ER is awash in Christmas casualties.