Unforgotten

When a headless body is found on a scrapheap, the team identify the victim as Matthew Walsh. Cassie wants to retire, but in order to get her full pension, she is forced to return to work.

Cassie and Sunny identify four suspects who trained as police probationers together, and find that two of them are still serving police officers. They have no luck finding the rest of the body, and they make the discovery of Walsh's body public.

Cassie and Sunny interview each of the four suspects, who all deny knowing the victim. Bouting discovers Walsh was cautioned three weeks before his death and believes it was with Ram, whilst Collier manages to locate the rest of Walsh's body.

Cassie and Sunny discover Walsh was chased by all four suspects on the night in question. Willets realizes Fiona's blood sample may have been deliberately lost by Liz. The pathologist identifies a cause of death implying Walsh was murdered.

Cassie and Sunny interview two of the suspects again and get closer to the truth of what happened to Walsh. Balcombe believes she may have found the cause of death. Unexpectedly, things take a devastating turn for Cassie.

Despite a tragic turn of events, Sunny and the team narrow down the suspects. They must find conclusive proof of who the murder weapon belonged to in order to succeed in bringing Walsh's killer to justice.