A frantic Jack carries out forensic examinations on the spot where Nikki disappeared. With Thomas at the airport ready to come out and help, but still 24 hours away and no leads left to follow, Jack receives a text message containing a mysterious phone number.However when Jack calls through, expecting to hear from Nikki's captors, he is shocked at who answers the phone. Can Jack save Nikki?

Nikki travels to Mexico to attend the funeral of Luisa, a former intern at the Lyell Centre who was murdered in a carjacking in her native country. Nikki soon stumbles across the post mortem report and realises that the body is not Luisa's. There's been some kind of mistake - or is this something more sinister?

Assisted by Dr Eva Vasquez and fired up with the idea that Luisa might still be alive, Nikki and Jack trace her last known movements and are led to a farm where a cartel massacre was carried out, where they start to perform makeshift post-mortem examinations.

By now, Nikki and Jack are gaining the wrong kind of attention. And when Nikki goes missing, Jack is forced to make decisions that will end in life or death…

Examining the contents of Liam's phone, Clarissa has found a longer version of the video and sees a flash of Paul's face as he peers from the stairs. Retrieving Paul's laptop, Clarissa takes it to Max's lab and finds reams of communication between Paul and another person, under pseudonyms, which starts to unravel the mystery of the Billingsgate killings.

Meanwhile, Clarissa is amused to see Thomas' nose put out of joint and Jack soon feels paranoid that Max is poaching Clarissa for his own lab. Will Clarissa remain with the Lyell team?

Father and son Bill and Frankie McAteer are killed in a horrific car accident on their way home from work at Billingsgate Market. Nikki and Jack arrive at the scene of the crash to meet DS Jodie Tanner, and to discover Frankie's body still in the car but riddled with bullets. Whoever was driving the SUV had a gun.

Back at the Lyell centre, Nikki's post mortem examinations suggest that Frankie was the target, rather than Bill. Clarissa and Max discover a deleted video on a mobile phone showing a sexual encounter between Frankie, his girlfriend Becky and best friend Liam, which was posted on a revenge porn website. However when Liam is also killed, the video becomes the key to the killings.

When Nikki and Tanner visit Becky, her flatmate Paul enters and she bursts into tears about the murder. But Paul looks like he has worries of his own…

Meanwhile, Clarissa's husband Max is an expert in the fast-developing field of digital forensics and lends some equipment to help crack Frankie's seemingly-empty phone, his arrival causing an icy reaction from both Thomas and Jack.

After bereaved mother Ali attacks suspect Aaron, Nikki is under fire for leaking information. Jack and Thomas must bridge internal divisions to track down the killer.

A woman's body found floating in the Thames leads Nikki and Jack to a riverside community scarred by grief after the disappearance of a teenage girl three years ago.

In order to discover the truth between these two cases, Nikki visits disgraced pathologist Mike Liston, convicted of falsifying pathology reports, to find the truth about a cold case that holds the key to the mystery in the form of a 20 year-old DNA profile…

It's a sunny May bank holiday and the newspapers are abuzz with the news of the disappearance of a young schoolteacher.

Investigating officer DCI Andy Steemson asks Nikki and Jack to examine the small blood traces, bike tracks and a charred cake in the oven in the house. This was no planned disappearance.

Meanwhile, Thomas is called to the site of the murder of an ex-junkie and a petty criminal with the opposite circumstances. The body has been thrown from the top of a flyover and DS Maureen Steele, a police officer with a drink problem, has been given the case. Bumping up against Steele's dismissive attitude, Thomas becomes determined to win justice for the victim - and ultimately forms an unlikely alliance.

However when a body is found in a pond off the M25, Nikki and Jack make the discovery that the deaths are linked. But what is the link between these two disparate cases?

Breaking into the van, Jack and Nikki are met by a horrifying sight, as Nikki realises that Akka's mother is among the dead.

Meanwhile, Sosa's van is arriving into Dover Ferry Port. The illegal passengers are nearly caught when Border Force officers ask to inspect the van, but a corrupt official overrules his employees and wave the van through.

Following the trail of messages between the gang members, Yusuf realises that another of his smuggling partners, Abdul Wilson, has been using the system to extort money from the desperate family members of the migrants, and then leaving the migrants to die after their arrival in England.

With Sosa in another white van, is her life in danger?

When a people smuggler is found dead in the City, Nikki must delve into London's illegal immigrant community. She meets a vulnerable Syrian teen called Akka who is in need of help, putting Nikki in a moral dilemma - and the killer is still on the loose.