Unforgotten, Series 1 - 4

The discovery of a skeleton in the cellar of a demolished building launches a murder hunt, headed up by DCI Cassie Stuart and DS Sunny Khan.

Having identified the body in the cellar, the detectives must work out how a government advisor, a priest, a bookkeeper and a housewife are related to the victim's death.

Cassie and Sunny dig deeper into the lives of two of the people mentioned in the diary, beginning with Father Robert Greaves, who remembers Jimmy fondly.

As the investigation into the cold-case murder continues, the forensic team discovers that the marks on the victim's body are consistent with known gangland torture methods.

As Cassie and Sunny continue their investigation into the cold-case murder, the net tightens around the people whose names were found in the victim's diary.

Father Robert's revelations prove to have lasting repercussions, especially for Caroline when she goes into premature labour.

Detectives Cassie and Sunny, find themselves thrown into another historic murder case with the discovery of a body. This time it's the remains of a middle-aged man found in a suitcase.

With their victim identified, Cassie and Sunny begin to gather more information about David Walker by talking to his ex-wife, DI Tessa Nixon, who reveals he suffered from depression.

Sunny makes further investigations into David Walker's life that suggest he was a troubled man with a number of issues. Marion has a prickly chat with Cassie about her past.

Marion jeopardises her marriage by refusing to open up about the past to her husband, Colin is blackmailed even further and the secrets of Sara's past push her family to the limit.

Cassie focuses on Brentford house and the theory that some of the suspects may have been abused at the gatherings there. Marion is questioned again after Sinead's allegation.

With the suspects in the murder of David Walker all having either a motive, opportunity or connection to the victim, Cassie and Sunny are left with a massive puzzle to solve.

When human remains are found buried in the central reservation of the M1. Cassie and Sunny begin the task of identifying them.

The search for what happened to Hayley begins as the team travel down to Middenham to meet her family.

Cassie and Sunny begin interviewing the four male occupants of The Spinney over the millennium, who all have fairly consistent accounts of the time spent in Middenham. The rest of the Bishop Street Station team look at the timelines and leads from the original investigation.

Cassie and Sunny suspect that the men all colluded in lying about their version of events for that evening, but why? The press begin to circle as they find out that James has been questioned in connection to the Hayley Reid case.

Cassie and Sunny finally get closer to some truth about the night Hayley disappeared and the case takes a devastating turn for Cassie.

Under the glare of media spotlights, the team race to find the evidence to prove the identity of Hayley's killer.

Sunny is called to a dump sight in Haringey, where a headless body has been found amongst the freezers. Meanwhile, Cassie has been on medical leave and doesn't want to go back to do her final three months.

As Sunny and Cassie investigate they find that a graduating class of police officers could all be connecting to the case- some are still serving in the force.

Cassie and Sunny interview the four suspects, who all deny knowing the victim. Boulting discovers Walsh was cautioned three weeks before his death and believes it was with Ram, while 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. Will they find conclusive proof of who the murder weapon belonged and succeed in bringing Walsh's killer to justice?

Dr Peter Dean, forensic advisor, talks us through the discovery and recovery of skeletal remains and how Unforgotten makes this as authentic as possible.

The cast and crew of Unforgotten provide an introduction to the universal themes of relationships and betrayal in this murder mystery series.

A look at how this series has progressed from Series 1.

The cast discuss the impact of living a lie.

The cast look at the relationship between the characters in this series.

A look at the set design within the show.

Sam Ives, Art Finisher, explains how the props were created.

A look behind the flashback scenes which provider the viewer with clues.

Sunny reveals the contents of his rucksack!

DCI Cassie Stuart and DI Sunil 'Sunny' Khan reunite to solve another historical crime, their first since they chose to walk away from a case in which victims of child sex abuse had worked together to murder their abusers. This new investigation sees four men under scrutiny when the body of a teenage girl is found at a building site off the M1 motorway. It's revealed that she's been missing since the turn of the millennium and it's up to Cassie and Sunny to figure out whether any of the men had anything to do with her death.

The writer, director and cast discuss the background to the programme.

Detailed insight into the filming of this series' opening scene.

A look at some of the locations features in the series.

How integral social media is to our lives.

The actors playing the key suspects in the series discuss their characters.