Critical will be one story, in one place, in one hour - a real-time medical and emotional roller-coaster ride in which every second counts during the most life-threatening hour of a patient's treatment. Lennie James (The Walking Dead, Line of Duty) will lead an ensemble playing locum trauma consultant Glen Boyle. Catherine Walker (Strike Back) plays trauma registrar Fiona Lomas with Claire Skinner (Outnumbered) playing trauma consultant Lorraine Rappaport. Finally, junior doctor Dr. "Harry" Bennett-Edwardes is played by Kimberley Nixon (Fresh Meat).