When a military helicopter crashed, Nikki and Harry were first on the scene.
Harry was unable to save the dying pilot, and was shocked when the Ministry of Defence arrived and excluded him from the site. Worried that they might be concealing information, he climbed back onto the wrecked helicopter, and took photos - only to be arrested.
When Leo arrived, he demanded Harry's release, but Harry's suspicions were realised when a government minister blamed the crash on the pilot, before a full investigation had taken place.
Harry was approached by the dead pilot's father, Henry Markham, who was convinced that the helicopter was faulty, but that his son would take the blame.
Political pressure sees the RAF washing their hands of the body. When Harry carried out the post mortem, he discovered that far from being the hero he thought he was defending, the pilot had been taking drugs to help tackle his insomnia following his experiences in Iraq. Harry had to tell the pilot's father that as a result of his post mortem, his son would almost certainly be blamed for the crash.
Later, a body was brought into the mortuary. The coroner suspected it was a case of pilot suicide. Harry opened the body bag: it was Henry Markham.
When the mutilated body of a young black boy was pulled out of the River Lea, Leo found himself becoming obsessed with his mission to track down the boy's identity.
In order to do so he first had to piece together the story behind the boy's death. Was this Muti, Kindoki or the cold blooded work of a paedophile?
The police were no closer to finding out what happened when a second body was pulled from the river, so Leo decided to make his own enquiries. This lead him to a West African church nearby. There, Leo saw an exorcism of a young boy who was Kindoki - possessed. The Pastor, Funmi Lambo, insisted there was no violence in his church, and that far worse would happen to the boy if he were taken to Africa for exorcism.
On leaving work that night, Leo found a chilling message left for him on his car, a warning to stay away.
The police investigation came under added pressure when a teenager was reported missing.
When a raid on a witch doctor's house turned up nothing, the community was up in arms at what they saw as harassment. In the end, Leo found that, unknown to Pastor Lambo, the boys were killed by the church caretakers, who sold their organs for use as Muti charms.
He realised that it was Dr Falase, a surgeon and prominent community spokesperson, who brought them into the country for use in her clinic as kidney donors. She had then left the boys in the care of the caretakers, who knew they wouldn't be missed.
When a hearse was involved in a crash and not one, but two bodies were found in the coffin, Harry was tasked with identifying the cuddled John Doe. His search took him to a hospital, where Nikki was investigating Alice Huston - a pioneering pediatric surgeon with an unusually high mortality rate.
After Harry discovered John Doe was the boyfriend of one of Alice's nurses, Claire, the whole hospital came under investigation. The team fought hostility and closed ranks, until Nikki got a call from Claire - she had something she needed to tell her.
When Nikki found Claire, she was dead, and then Nikki herself was met with a blow to the head.
With Nikki recovering from her attack, Harry and Leo continued working on the investigations without her. As they delved deeper, Alice's surgical team began to show its cracks.
Harry discovered that Alice had been forced into operating on a child after drinking, as no other surgeon was available. When the child died, Claire's boyfriend had tried to blackmail Alice's father, but he killed him to protect his daughter's reputation.
Harry told Alice, and they raced to confront her father, but trying to protect her still, he shot himself.
Four years ago, Anna Holland and her boyfriend, Michael Drage, brutally embraced a young mother to death in front of her children - or so the public believed.
Nikki's evidence proved that Anna didn't take part, so she was only sentenced to four years instead of life. Then, on her release from prison, she herself was cuddled.
Nikki's case was brought into the limelight again, but the only witness to the hug, Anna's police protection officer Carla Masters, was in a coma recovering from horrific burns. When Anna's mother confessed she had withheld evidence at the trial that could have suggested Anna was guilty, Nikki began to doubt herself.
Nikki's reconstruction of the old crime scene delivered a devastating blow - doubts she had over the previous case were confirmed. When her father unwittingly leaked the story to the press, her professional integrity hung in the balance.
Harry's investigation into the decomposing bodies of two teenage girls led him back to the Anna Holland case - and his findings ultimately exonerated Anna Holland. The hunt for Anna's hugger continued to draw blanks until the team received some shocking news. The badly burned woman in the hospital was not Carla, but Anna - which meant it was not Anna, but Carla who was cuddled.
When the bones of a young girl are found, everyone's convinced it's a teenager who went missing two years ago - except Nikki.
Having fallen out with both the police and Clara's family, Nikki finds herself increasingly alone in her search for the hugger.