Following the deaths of Sgt. Matthew Boyden and an unidentified black man in a drive-by shooting, the gunman makes a speedy getaway leaving the team with no idea which man was the intended target. Meanwhile, his own drug addicted daughter, Amy, hears the news from a custody cell back at the nick. Still in shock, evidence collected from his daughter and colleagues lead the team to discover Boyden wasn't always on the right side of the law. Sure he may have had a few skeletons in his closet, but did anyone hold a killer grudge? The investigation takes a surprising turn when Sam is brought in for questioning – her underage daughter has been involved with Boyden and she is now a suspect in the enquiry.

Vivien investigates the murder of a young woman whose remains have been found preserved in a concrete tomb at a demolition site. The only clues to her identity are a healed scar along her left hand and a puncture mark at the base of her spine from a medical procedure. The investigation leads to a three-year-old missing persons case in which a young girl vanished from her parents' pub without trace. When the autopsy confirms it is the same missing girl, Vivien has to break the news of her death to her distraught parents. The strongest lead is a mysterious photograph of their daughter with an unidentified man. And then the pathologist reveals she was in the early stages of pregnancy.

The dismembered body of a small child is found on a Thames rubbish barge. A painstaking search through layers of decaying rubbish reveals some clues but a discovery during the post mortem is even more disturbing. The little boy's heart has been crudely removed from his body and it looks like his murder could be African ritualistic killing. The murdered child's parents have logged a missing persons report, but their priest prevents Vivien from making contact. Offering to act as their interpreter, the priest speaks on their behalf, but Vivien soon realises the parents do, in fact, speak English. Does the priest know more about the child's murder than he is letting on? And where is their younger child Francis?

The team are called out to a double murder on a rundown housing estate. A middle-aged teacher, Martin Ramsey, has been pushed from his third floor window, and an old homeless man, Nelson Fairgrave, is found floating in a nearby lake – but what is the connection between the two men? A promising line of enquiry opens up when the police find out Ramsey was being intimidated by an ex-pupil, but there is little information to be had about the homeless man. When the police find several different trainer prints near to the lakeside they know they are looking for more than one man, but who would have wanted to kill Nelson Fairgrave, and why has Ramsey's computer been tampered with?

When the body of Penny Wake, a young red-haired housewife, is found in undergrowth by a mother and son out jogging, Vivien and the team are called in to investigate her death. There are no signs of a struggle but her body has been cleaned inside and out with bleach, and the team know they are looking for a calculating and forensically aware killer. Her husband, Neil, has no alibi for the night of her murder and is consequently their prime suspect, but when another red-haired woman is brought into the local hospital drugged and disorientated, a new line of enquiry opens up for the team which leads them to one man's terrible and dark secret. The question is, is he prepared to kill again?

Natasha McKay is the woman with everything – a glamorous modelling career and a rich property developer for a husband. But when her disfigured body washes up on the banks of the Thames it becomes apparent that Natasha's life was not all that it seemed. An ex-school friend comes forward to come clean about his affair with Natasha: they were in love and they were going to marry. But when the team interview her husband Dennis McKay, he has an alibi for the night of her disappearance. Soon enough, a ring of faked pornographic photographs and the gambling debts of one of McKay's co-workers reveal the true motive for murder – and Vivien is sure that the evidence is strong enough to warrant an arrest.

When convicted child sex offender Dominic Moreton is bludgeoned to death in his own home, it looks like the work of vigilantes. The team's most promising lead in the enquiry is a phone call that the victim made to a possible associate, Peter Taylor. Dominic had been calling Peter on a regular basis, so when they search his house and find photos of Dominic with Peter's wife, it throws up all manner of questions. Soon they discover that Dominic and Peter are the same person – Peter was an undercover SO10 officer – and that he recorded his own murder on his wife's answer machine. Vivien realises that if they can decipher the background noise on the tape, they might be able to discover what really happened to Peter.

Tensions run high in the Bangladeshi Community when the body of journalist Ellen Merrick is found dead in a disused shop in the local market place. Witnesses are reluctant to come forward to the police so the only clue the team have to work with is a bloody trainer print and some fibres from a nylon tracksuit at the crime scene. The team urgently need to find out what story Ellen was working on at the time of her death, but newspaper colleagues are reluctant to co-operate and with silence from the local community, Vivien needs to move quickly if she is to catch Ellen's killer, but she certainly doesn't count on another case opening up before her eyes.

The team are called to the scene of a violent street stabbing, in which young Lithuanian Ed Villarin, collapses and dies in the street after being stabbed with an ice pick during a game of 'phone tag', in which strangers join the game over the internet and must 'hunt' and photograph the 'target' with their mobile phone. Initially, Trevor suspects that outside influences such as Ed's involvement with the importation of stolen mobile phones, and a violent argument with a former co-worker are the motives behind his murder. However, convinced that the answer lies somewhere within the game, Simon attempts to track down the controller. Rosie and Eva arrive to find for him, the next level of the game is the kill.

The team uncover a vipers' nest of malpractice and drug dealing after a popular hospital registrar, Karl Anderson, is pushed off a hospital roof into a busy social gathering down below. With many suspects to question, and a number of leads to follow, the team soon find themselves under pressure to catch the killer before he strikes again. A search of Karl's house discovers a seventeen-year-old girl's medical file hidden between a collection of old LPs, and the discovery that she died just five days after a routine appendix operation. Suspecting that the hospital's clinical lead, Dr. Stuart Masters, may have botched the operation in order to save time, gives the team a perfect motive for his murder.

The pressure is on the team as the net tightens to secure a result when professional football player Sean Reynolds is found beaten to death near a local park. Suspicion falls on both his close and estranged family – as well as angry group of fans who were furious about his decision to leave the club – but no secure leads or forensic evidence can lead to a concrete conviction. The key to the entire case soon boils down to whether Sean's wife or his mother-in-law was the driver of her Mercedes Coupe, which is spotted on CCTV following Sean to the location of his death. Simon's interview techniques prove to be the catalyst for solving the case – but he's not convinced of who is responsible for murder.

Sexual tension becomes rife among the team when a crime scene colleague is found strangled in her flat, with her underwear having been placed in her mouth. The initial investigation becomes complicated when a second victim is found dead in similar circumstances. However, there are a number of indiscrepencies with the second killing that make it out to look more like a 'copycat' rather than the same killer – but the team are baffled as to how the killer got hold of the information, when it hasn't been released to the press. When CCTV shows Trevor accompanying the victim home, he soon becomes the prime suspect – but can his best friend and colleague Rosie prove that he is not capable of murder?