Leanne Wellings prepares to visit her grandfather, who resides in a convalescent home. She takes her two young children Rosie and Ethan, and calls up the stairs to her eldest daughter, Tanya, to join them. Tanya makes an excuse to avoid going. Leanne eventually leaves with Ethan and Rosie. Leanne rushes to collect a dog from the shelter before it closes. She then drives to her grandfather, new dog in tow, but stops at a layby to buy him some flowers from a van. A lorry draws up at the same time. The children lose sight of their mother as they sit in the car. Leanne does not return and the bewildered children start to walk away from the car.
Leanne's husband Matt works at a local gym. It is here that several of the characters connect with each other: Press Officer Defne ignores loner Kyle as he tries to make a conversation. In another scene, Leanne's parents, Barbara and John are introduced. The family slowly learn of Leanne's disappearance, and that Rosie and Ethan are now missing too. Kyle seems to have picked them up in a white van. The police begin the investigation, but the Press Officer feels there is a lack of support, and the DSI in charge is relatively new in the position.
Matt's best friend, Gary, is about to retire, and complains of not having enough pension to live on. Matt gets him a job at the gym where he works, and the police recruit him to spy on Matt, paying him for information.
The police begin a house to house investigation. Meanwhile, Beam wakes up Sarah, who has jet-lag and is disorientated. On learning the time from Beam, she dashes out of her flat, and opens a shed door to dump her rubbish. There, crouching in the darkness, she finds Ethan, and the dog. Ethan says that he was supposed to look after Rosie. Sarah is seen as a heroine for finding him. Ethan tells the police that his dog bit a man, who had a dirty white van. Kyle's mother Hazel becomes suspicious of his actions. His hand is damaged, and he begins to wash his white van every day despite previously never washing it.
Meanwhile journalist Josh smells a story, and persuades his editor to run a picture of attractive Leanne on their front page. Josh's is a small local newspaper, and he wants to run a more exciting story than golden weddings. He publishes Leanne's picture, despite getting the brush off from Defne, who is trying to keep the story relatively low profile. Josh takes photos for the paper at the home where Vic, Leanne's grandfather, lives. Josh manages to converse with Vic about his granddaughter. He eventually persuades Vic to loan him the key to his mobile home, in order to gather clues and background details. However, when he arrives at the mobile home, he is astonished to discover Rosie on the bed seemingly unharmed. He calls the police and takes pictures for his paper and dashes off to his office, leaving Rosie with the neighbours. However, Josh doesn't see Kyle who, on arriving at the mobile home in his white van, is arrested by the police.
Defne eventually persuades Matt to give a press conference, and Barbara agrees to speak as well. The press conference doesn't go well, and Josh asks Matt if he knew that Leanne was pregnant, having acquired the information from her grandfather. Matt, clearly shaken, walks out. It is left to Barbara to appeal to whoever has any information about Leanne's whereabouts. At first, she is calm, then she gives in to a scream of panic and grief in front of everyone. After the debacle, DSI Barclay is rapped by his superior for not participating and supporting the press. He remains aloof, but agrees to help.
Sarah is finding it hard to let go of Leanne's family, and starts seeing them regularly. Sarah attempts to start a relationship with Matt, but he rebuffs her advances, telling her that they can only be friends. She is upset at this, and eventually tells him her own traumatic past, in which her father murdered her mother, Sarah was 5 at the time. This seems to explain her rather unbalanced behaviour since finding Ethan.
Tanya has left to live with Barbara and John and expresses her feelings of guilt to John. She tells him that she didn't want to visit Vic because his room smelt. Tanya feels that Leanne's disappearance would've never happened if she'd joined them. John tries to reassure her. Eventually Tanya goes to stay with her dad in France. The police have a lead that Leanne may have started seeing her ex- husband, but they haven't followed it up. Barclay is obsessed with following the flower seller, a Bosnian, who may have links with illegal immigration from Macedonia. This frustrates the rest of the team.
After 28 days, DSI Barclay comes under scrutiny from his superiors in the Met as he has no leads on the case at all. They are about to submit a report and are asking the team questions. His colleague Amy is frustrated that he hasn't named a suspect. She accuses him of refusing to name Matt as a suspect because he's black. However, Barclay's superiors ordered him to lay off Matt. Barclay denies this. Later a body is found in the woods by the dog shelter owner, whilst out walking his dogs. The body is identified as Branko, the Macedonian illegal immigrant who sold flowers from a van, the van Leanne was buying flowers from when she disappeared.
On day 33, it is August Bank Holiday. Defne is taking part in the fun run and Beam is there to support her. Josh is there to cover the event for the paper. Simone, Sarah and Matt take the children to the fun run. Matt becomes overwhelmed by the crowds and he and Sarah go to her flat, leaving the children and the dog with Simone. They have sex, despite Matt's reluctance. Suddenly a boater on the lake spots a body in the water. After several days it is confirmed that the body is Leanne's.
Amy is about to retire, and her colleagues throw a party for her. She drunkenly gives a speech about not missing her colleagues. However, she is actually terrified at the prospect of life without her work. Barclay takes her home and sobers her up. Before she retires, the forensic lab does her one last favour, they identify the fibres under Leanne's fingernails as carpet. It becomes apparent to Barclay that Leanne, desperate to give a clue to her would be rescuers, deliberately scraped up the fibres so that they would be found. It was also established that she was alive when she was dumped in the lake. John is admitted to a psychiatric hospital, following an overdose. Barclay had warned him about seeing Leanne's body after 5 weeks underwater, and he's traumatised. Only Tanya comes to visit him, her true feelings for her grandfather shows, mirroring her mum's devotion to Vic, despite her protestations of "who needs love, anyway?" Barbara is furious at John, and refuses to see him. Beam is irritated by the dog shelter man, who insists on confessing to killing Leanne.
Kyle is in court, he is remanded in custody despite his pleas that he was regularly beaten by other inmates in prison. The judge refuses to remand him to his mother. Kyle manages to escape from the police van that was taking him back to prison. He's hit by a car, but continues on his way, eventually ending up at Rosie and Ethan's house, where they're being cared for by Sarah. Rosie is delighted to see him, and gives him a hug. He disappears before Sarah comes out and finds the children.
Gary finds Kyle at the gym and beats him viciously, telling him to be quiet. Matt tells the others to call the police, and then locks himself in the locker room with Kyle and Gary, where he demands to know if Kyle hurt Rosie. Kyle insists that he didn't, and says that it was all an accident. He and Branko ran a smuggling scheme bringing in untaxed cigarettes, and storing them at Vic's mobile home. Vic had let them use it as a favour for Hazel, Kyle's mother, who worked at the nursing home and was the only person who was kind to Vic. When Leanne stopped to buy the flowers, Kyle was in the back of the flower van with cigarettes and illegal cash, Leanne then started to shout at Branko that his cancer sticks were killing her grandfather. Branko attempted to shut her up, and Leanne hit her head, and fell unconscious. Terrified, Branko and Kyle threw her in the back of the van and drove off. When she recovered consciousness, she was concerned about her children, so Kyle went to pick them up in his white van. Ethan and the dog jumped out, but he took Rosie back to Vic's mobile home, where Branko had taken Leanne. Kyle insists that it was too late, and Leanne died, so he took her body and put it in the lake.
Matt tells him that it wasn't too late, that Leanne drowned when Kyle dumped her in the lake. Kyle is horrified and turns to Gary and shouts "You said she was dead!" Matt understands that it was Gary who killed Leanne, and attacks him. The police break in and take them all away, but Kyle dies of his injuries inflicted by Gary. Gary is charged with the deaths of Leanne, Branko and Kyle. The final scene is Matt with his three children at Leanne's grave . Sarah is nearby, but doesn't join the family as they walk away together.
