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.

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.