The first episode explodes onto TV screens with a man walking out of a hotel lift covered in blood and holding a fire extinguisher. He approaches the reception desk shouting that he has killed someone. As the terrified receptionist tries to ring 999, the man grabs the phone, but the police have been alerted and they're already racing to the scene. Cameras follow every twist and turn as detectives from the Major Crime Unit try to disentangle what really happened at the hotel close to Luton Airport, which has suddenly become a chaotic and bloody crime scene. This is real-life drama at its most intense. Throughout the series, cameras follow each case in forensic detail as the officers race against time to disentangle the evidence and build a case, which they then put to their suspects in interview.