While Hathaway takes time off to do volunteer work in Kosovo, painting an orphanage, Lewis is on his own. He pays a visit to Louise Cornish, the wife of his friend and former co-worker, Jack Cornish. Jack Cornish has deserted his wife and sons, and is rumoured to be romantically involved with Tara Faulkner – a big mistake, according to Chief Superintendent Innocent, as Tara's husband, Peter, is a well-known miscreant. Meanwhile, Jack is attending a dinner party at Peter and Tara's posh home, where tipsy guests engage in clever conversation but the undercurrent of tension suggests deeply rooted antagonism and secrets all around. For the caterers, Johnny Jay, his son Liam, and Liam's girlfriend Ruth, it's a relief to be sober. Johnny is a recovering alcoholic.
Lewis is called to investigate a body dumped by an isolated farm track; oddly, it was already embalmed. With his inexperienced temporary sidekick, constable Alex Gray, Lewis identifies the corpse as the elderly Neil Strickley, who, according to his doctor, Matt Whitby, died of cancer. But the undertaker, Brian Miller, protests that the corpse couldn't be Strickley – he was already cremated. The brutish Peter Faulkner owns a majority stake in Brian's funeral home but, when interviewed, he denies having been there for years. Lewis and Gray learn about the Faulkners' dinner party and note the guests: Matt Whitby (Tara's brother), Jack Cornish, the Millers, and lecturer Emma Barnes. Lewis wants to question Tara and Jack, but both are off the radar. Peter suggests that his wife left with Jack Cornish for her farmhouse in Croatia.
Liam Jay works for Brian Miller as a pallbearer and doing repatriations – bringing bodies back from abroad. He is a student of Emma Barnes', and is a patient of Matt Whitby's. When he sees something at the funeral home that shakes him up and he is questioned about losing Neil Strickley's body, he turns to Whitby for help. Whitby is quick to give him meds for his anxiety. The next day, Whitby is found dead at his desk, poisoned with formaldehyde. Lewis brings Peter in for questioning, accusing him of murdering his wife and swapping the body with Strickley's to be cremated, but is proved wrong when Tara appears at the station. Tara is deeply distraught about her brother's death. Liam is, too. He has been kicked out of school; he cannot depend on his father, whom he presumes is out of touch on a bender; and he can no longer get pills from his doctor, Whitby.
Lewis, still trying to find out who was cremated if not Strickley or Tara, now believes it to be Cornish, positing that Cornish looked too closely into the Faulkners' unsavoury business affairs and had to be killed. He goes looking for Liam and discovers the boy bloodied and unconscious in the funeral parlour's refrigeration room, on the edge of death.
With Liam recovering in intensive care, Lewis and Gray now have three mysteries, somehow connected, to solve: who was cremated in the coffin; who killed Matt Whitby; and who tried to kill Liam Jay. Surveillance footage shows Whitby at the funeral home the night before Stickley's fake funeral. Questioning Tara about Liam's attack, Lewis learns that she had never gone to Croatia with Jack; she went, alone, to Barcelona.
Lewis ventures with Hobson to Ruth's houseboat to question her, knowing that she, too, was at the Faulkners' dinner party. They find the boat on fire and rescue the unconscious girl. Lewis now suspects that Liam's drunk father, Johnny Jay, killed Cornish, then Whitby, then went to the farmhouse in Croatia to hide out. They call on the nearby Hathaway to investigate. But when Hathaway visits the farmhouse, he comes face-to-face with Jack Cornish, who then vanishes. Hathaway discovers that the Croatian farmhouse is actually a crystal meth factory. The Faulkners and Whitby were running a drug smuggling operation, importing crystal meth inside of the expatriate corpses!
Cornish, now returned to the UK, admits to his affair with Tara Faulkner, but denies knowledge of a drug ring. Tara admits that Johnny discovered that his son was being used to import drugs. When he threatened to go to the police, Peter killed him and swapped the bodies with the help of Whitby. Peter then killed Whitby because the doctor couldn't be trusted. He tried to kill Liam and Ruth because he thought they knew too much. Miller was part of the drug ring but didn't know about the murders. Cornish manages to elude charges for any of the crimes.