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. Detectives initially question whether the men have attacked one other, and take to the streets to search for witnesses. People are reluctant to talk, until a local homeless man comes forward claiming that a drug dealer was involved in the attack. A forensic search of the crime scene by a dog specially trained to detect blood reveals a new trail that leads police to an address believed to be used by the suspect. The firearms unit are mobilised, but will they get there before it’s too late?