In Northumberland, England's northernmost county, single mother Julie Armstrong (Gina McKee) returns home from a date only to find her 15-year-old son Luke (Sam Fender) strangled to death and left in her bathtub, surrounded by wildflowers and candles. On the case is Detective Chief Inspector Vera Stanhope (Brenda Blethyn) and her associates Detective Superintendent Joe Ashworth (David Leon) and Detective Constable Holly Lawson (Wumni Mosaku). Via their forensics expert Billy Cartwright (Paul Ritter), they are able to deduce that Luke was killed with a rope before being placed in the bathtub and that the killer came in through the kitchen window. Vera learns a terrible truth from Julie that, only four months earlier, Luke had witnessed his best friend Tommy Sharp drown in the sea, and he had been despondent ever since. Before he died, he received a letter that included nothing but a pressed flower, the same kind found around his corpse.
In another part of town, Felicity Calvert (Juliet Aubrey) welcomes home her son James (Louis Shergold) after a long day of school, and he has brought his teacher home with him. It seems that this lovely young woman, Lily Marsh (Sam Neale), is between homes and has heard from James that the Calverts have a beach hut they're looking to rent out.
Back at headquarters, Vera and her team look for any possible leads, focusing on Tommy's drowning. Using an eyewitness report, Luke had tried to do everything in his power to save Tommy from being taken out by the current but failed, leading to the coroner to label the death as "misadventure." Watching video footage taken at the beachside memorial at the same place where Tommy drowned, they notice that the exact same flowers used at Luke's murder site were also strewn on the water. Their suspicion? Focus on Tommy's grieving father Davy (Craig Conway), an ex-con who has been living off the grid. They find Davy hiding out at the ruins of a castle overlooking the beach where Tommy died, but although they have reports that Davy had been spying on Luke's home, they have nothing to put him away.
The plot thickens when a group of birdwatching friends -- including Felicity's husband Peter (Murray Head), womanizer and Julie's current boyfriend Gary (Neil Armstrong), widower Sam (Patrick Toomey), and doting Clive (Paul Higgins) -- celebrate their friendship when young James wanders off and discovers Lily, strangled and deposited in a rock pool, once again surrounded by wildflowers. A link has been established, and it must involve as least one of the birdwatching friends.
Visiting Lily's apartment, Vera and Joe learn that while she was behind on rent, there was no indication that she was ever looking to move out. When they check her post, they find another letter -- unsealed -- also containing another pressed flower. Luke and Lily were targeted by somebody local, but whom? Vera and Joe go have a word with Lily's ex-boyfriend, who tells them that while Lily is a fun person to be around, she can be obsessive and clingy, and when he had to break up with her to focus on his career, she became near-psychotic. Going through Lily's bank records, Vera discovers mysterious monthly deposits into her account from an unknown source, like from some kind of "sugar daddy," but the payments had stopped six weeks earlier. Was she having an affair? Was Lily only pretending to be interested in the Calverts' beach hut in order to spy on Peter?
While Joe follows up with Felicity and begins to suspect that she herself may have a sordid past with other members of the birdwatching group, Vera makes big strides in the case when she gets to have a private word with Laura Armstrong (Gabrielle Ross), Luke's younger teenage sister. The details come pouring out: Tommy, quite the shutterbug, was having a secret relationship with Laura. Tommy showed Laura pictures he had taken, in secret, of Lily and an older man making love in the beach hut, and he planned on using this picture as blackmail. A few weeks later, Tommy and Luke got into an argument, prompting Luke to throw Tommy's camera into the water. And thus, this is how Tommy drowned. Thanks to a stroke of good luck, the camera in question was found in nearby Blythe and is already in police evidence. Using a similar camera, Vera goes to the castle ruins, points it at the beach community, and is able to get a clear picture of Felicity through a window.
The case goes into hyperdrive when Laura, after receiving the third flower-pressed letter, turns up missing. Knowing that all the victims have been placed in and around bodies of water, they go to the beach and find Davy there, dead from a head wound, near one of Laura's shoes. Vera doesn't think him the culprit, though, putting forth that the grieving man may have in fact been trying to save Laura. Put back under more intense interrogation, Peter finally admits to having an affair with Lily, but an airtight alibi keeps him from arrest.
Something clicks in Vera. She rechecks the eyewitness report for Tommy's death, knowing now that it is one big lie thanks to Laura's details. Suddenly, Vera knows not only who the culprit is, but where he's keeping Laura. Returning to the ruins, Vera and Joe find Clive holding Laura at bay with a net tied around her neck. Clive confesses: He didn't want to see his friend Peter's life ruined by his affair with Lily, so he took it upon himself to tie up the loose ends. Knowing that it's all over, Clive climbs to the top of the ruins, holding one end of the net, and jumps, strangling Laura in the process. Joe cuts the net just in time, releasing Laura and causing Clive to plummet into the rocky sea below.
Hey! I Know That Actor!
Brenda Blethyn, who plays DCI Vera Stanhope, is a BAFTA-winning and Oscar-nominated actress who has appeared in such films as "Little Voice," "Pride & Prejudice," "Atonement," and "Lovely & Amazing," but she is best known for her rousing performance as Cynthia Purley in Mike Leigh's "Secrets & Lies."
Murray Head, who plays the philandering Peter Calvert, is known for his international hit "One Night in Bangkok" and his role as Judas in the original concept recording of Andrew Lloyd Webber's "Jesus Christ Superstar." He is the older brother of "Buffy" star Anthony Head.
Gina McKee, who portrays grieving mother Julie Armstrong, is a renowned character actress both in such films as "Notting Hill," "Croupier," "MirrorMask," and "In the Loop" and on such television programs as "The Forsythe Saga," "Waking the Dead," and "The Borgias."