When a dead body is discovered at a warehouse, DCI Gene Hunt is quick to dismiss the death of Martin Kennedy as suicide, as Ashes To Ashes continues. However, with signs of a struggle and a massive blow to the head, the CID team find themselves involved in a murder investigation.

Feisty DI Alex Drake soon uncovers an intriguing piece of evidence: a piece of paper with a code. Leaving Custody Sergeant Viv with the task of solving the puzzle, Gene and the rest of the team head out to do the “real work”.

The investigation leads the team to a feminist socialist group, the Revolutionary Workers Front (RWF). It’s not long before Gene has every woman involved in the group carted down to the station. Chris, meanwhile, tries to impress Shaz with his new-found feminist knowledge and Ray is off on a date with a blonde communist.

Then Viv cracks the code and the evidence starts to fit together.

It seems that Kennedy had been stealing information about a nuclear weapons programme, ARTIMIS, from a secret Government facility called Edgehampton, and supplying them to the leader of the RWF.

Things get even murkier when Alex’s mother, Caroline, is drawn into the investigation. Kennedy has some incriminating photos of her, which puts Caroline firmly in the frame as a suspect in Gene’s eyes.

Later, a fake security pass gets Gene and Alex inside Edgehampton. A close shave with security leaves them locked inside a vault with no light or fresh air and the temperature rising.

As Gene and Alex face up to the reality of their situation, their undeniable chemistry threatens to boil over.