Episode one follows the investigation into the murder of 36-year-old Courtney Valentine-Brown, who was found stabbed in a flat in Southend-on-Sea. The episode spans the critical first two days of the investigation as a team of detectives and specialists work around the clock to catch the killers. The episode opens with senior investigating officer Stuart on his way to the crime scene. Inside, forensics get to work piecing together what may have happened and who was involved based on the extensive blood spatter in the flat. In a briefing at HQ, the team are given a variety of tasks before they scatter in the quest to find evidence. As the murder happened behind closed doors, there are no eyewitnesses and no CCTV, so they start from scratch trying to unlock clues and uncover leads. The first breakthrough emerges when a witness comes forward saying she saw four people enter the flat just before the murder. She recognises them as Kelly King (the flat owner), Ian Slater (her boyfriend) and two unknown men. With two suspect names, the investigation gathers pace. Operational Support are called in to lead the search for King and Slater. They eventually track King down and arrest her, but Slater is nowhere to be found. The manhunt steps up a gear with Steve Robson, a manhunt specialist from the Serious and Organised Crime Unit, deployed. Steve works proactively to hunt Slater down. He visits a range of Slater's associates, operating on the basis that if you rattle enough family and friends, then the suspect will eventually appear.

This episode follows the continuing investigation into the murder of 36-year-old Courtney Valentine-Brown. Over days three to six of the investigation, detectives, forensics and specialists track down those responsible for Courtney's death. On arrest and interview, one suspect, Ian Slater, names another, Alex Stephens, who he claims is responsible for the killing. A manhunt ensues for Stephens, and in a race against the clock, the team must gather enough evidence to charge or release.

The investigation into the murder of Courtney Valentine-Brown concludes. With one suspect outstanding, one on bail and one in custody, can the team of detectives and specialists secure enough evidence to charge them with murder? This episode also follows the investigation into the killing of June Knight, an elderly lady with dementia whose son is arrested on suspicion of her murder.

Episode four follows detectives and specialists as they investigate a double stabbing in Colchester's homeless community that leaves one victim, Carl Hopkins, dead - and the other seriously injured.

Episode five continues to follow the investigation into the killing of Carl Hopkins in Colchester. As the case enters its third day, the hunt is on for the unidentified murder suspect.

A quiet estate in Shrewsbury is the scene of a horrific killing when 23-year-old delivery driver Aurman Singh is ambushed and fatally assaulted in broad daylight. West Mercia Police begin a major manhunt to track down his killers.