What if one moment – one split second – changed everything? When a firearms officer shoots a suspect dead and wounds another, who later dies in hospital, the official line is that the sun was in her eyes. Her body cam failed. Known only as Officer X, her anonymity is meant to protect her – until a judge releases her name and a media storm erupts. DSI Jack Dylan and DI Charley Mann are called in to determine whether it was a justifiable use of force – or something darker. And when it's revealed that Officer X knew the victim, and her brother died of a drug overdose linked to the same woman, the case becomes charged with personal and political tension. As pressure mounts, a vulnerable witness dies and a lost phone surfaces with a photograph and a message that could unravel everything – and reveal the truth about what happened that day. Split Second brings Dylan and Mann together for the first time, in an investigation that will test their instincts, their loyalties and the limits of justice itself, as both detectives must decide how far they'll go – and what they're willing to sacrifice – to uncover the truth.