First broadcast 16/17 September, 2002.
Problems and conspiracy theories abound when the team re-investigate the murder of Katherine Reed, a case previously handled by one of Boyd’s old flames, DI Jess Worrall.
Notable guest stars: Corin Redgrave, Patricia Hodge, Ruth Gemmell.
The one where… Boyd shows off his tap-dancing skills and we meet his ex-girlfriend, Jess Worrall (played by Ruth Gemmell, who appears twice more in later episodes as Linda Cummings).
First broadcast 18/19 July, 2004.
When the body of a suspected terrorist is found in the stolen car of a former Home Secretary, Boyd and his team soon find themselves involved in the shadowy world of the Security Services.
Notable guest stars: Oliver Cotton, Frances de la Tour, Timothy West (father of Samuel West).
The one where… Boyd calls Grace “Gladys”.
First broadcast 14/15 January, 2007.
Trying to avoid a diplomatic incident, the Foreign Office task the CCU with finding the skull of the Mahdi, which was taken as a war trophy in the 19th century. In a parallel investigation, the team try to identify the murderer of Omar Jaffiri, who was allegedly tortured on behalf of the British security services.
Notable guest stars: Graham Crowden.
The one where… everyone spends an awful lot of time looking at skulls.
First broadcast 5/6 May, 2008.
The mummified body of what initially appears to be a skinhead is found, but as the investigation progresses it becomes clear he was not what he seemed. The team continue to concentrate on his apparent right wing political connections as the true reason for his murder unfolds.
Notable guest stars: Philip Whitchurch, Jo Woodcock, Russell Boulter.
The one where… Stella worries about HIV after assaulting a suspect with AIDS and Boyd (hypocritically) reprimands her for her conduct. Boyd is briefly reunited with his homeless, drug-addicted son, who begs to be released from the secure psychiatric unit his father has committed him to.
First broadcast 27/28 March, 2011.
When the body of Piers Kennedy, an ex-serviceman turned peace campaigner, is found in the sewers close to the Houses of Parliament, Boyd is quickly visited by MI5. He is warned not to share classified information with Grace, who was once on a government watch list. Things get more complicated when it seems that one of her former lovers, Murray Stuart, was somehow involved in the events that culminated in Kennedy’s disappearance.
Notable guest stars: John McArdle, Jack Shepherd, Penny Downie.
The one where… Grace’s activist past is revealed, she gets injured going to meet Murray at Boyd’s insistence, and new team member Sarah Cavendish sets Boyd’s downfall in motion.