Caspar Moss is a rugged army veteran, no-nonsense Northerner and lead Detective at the Met police. He and Rosa have a flirtatious but professional relationship; they knew each other from a case years ago involving one of Rosa’s patients. Yet Caspar is also one of Surgeon X’s primary antagonists; she has recently come on the radar of the Met police as her practice has been growing. He served in the army and saw action in Berlin where he fought against ISIS in 2025. His wartime experiences and injuries will come back to haunt him.