Driven to desperate measures, nurse Cath Hardacre (Jodie Whittaker) steals the identity of her best friend, an A&E doctor and finds work in a struggling emergency department. It's not long before she starts to enjoy the trappings that come with her new job and Cath soon finds herself falling for a fellow doctor. With her dream job and the perfect man, she buries herself in her imposter Persona, until her old life threatens to shatter her new existence and she's forced to go to increasingly desperate methods to cover up her lies. Will her lack of skills have deadly consequences? How can she be in a relationship when she can't be herself? How can she keep hold of the perfect life when she is living a lie?