Set during the early weeks of the COVID-19 lockdown in Dublin in spring 2020, the novel unfolds across three interwoven timelines: a present-day police investigation, a countdown tracing the weeks leading up to a death, and flashbacks exposing hidden motives behind a seemingly chance romance.
The present-day timeline opens at The Crossings, a modern apartment complex near Dublin's city centre, where residents are roused at dawn by a fire alarm. Two uniformed Gardaí, members of Ireland's national police force, stand in the courtyard. Gillian Fannin, a resident of apartment four who functions as the complex's self-appointed watchdog, directs them toward a ground-floor unit. No one knows who lives there.
The countdown begins 56 days earlier, when Ciara and Oliver nearly collide in a supermarket checkout queue. Ciara, in her mid-twenties and wearing a tech-company lanyard, is immediately struck by Oliver's attractiveness. He approaches her outside and compliments her canvas tote bag, which features a Space Shuttle image. They fall into conversation about space exploration, and Oliver, an architectural technologist at a firm called KB Studios, invites her for coffee by the canal. They exchange basics: Ciara says she is from Cork and has been in Dublin only a week; Oliver says he is from Kilkenny and recently arrived from London.
The same encounter, replayed from Oliver's perspective, reveals a different interior. He has noticed Ciara in the store for five consecutive days and suspects she may be a journalist tracking him. He goes by his mother's maiden name, Kennedy, having severed contact with nearly everyone from his past. He monitors online mentions of his real name and fears exposure. Despite resolving to cut contact, he cannot: He likes her and hates the loneliness of hiding.
Detective Inspector Leah Riordan, called Lee, and Detective Sergeant Karl Connolly are called to the scene. Inside apartment one, Lee finds the body: a male in advanced decomposition, face-down beneath the shower head, clothed in jeans and a T-shirt. The glass shower door is shattered, and a wound is visible near the left temple. In the medicine cabinet, Lee finds Rohypnol, a powerful tranquilliser.
The countdown continues as the relationship accelerates. On their first date, Ciara tells Oliver that secrets are destructive. Oliver, who is concealing a violent past, panics at the remark. On their next date, as the Taoiseach (Ireland's head of government) announces closures and social distancing measures, they end up at Oliver's apartment and sleep together. Ciara sees a thick scar running down his side; Oliver claims it came from a fight at 17, a lie. When the Taoiseach announces a formal lockdown confining everyone to their own household, Oliver asks Ciara to move in for two weeks. His perspective reveals calculation: Ciara has no social media or local connections, and no one knows they are together. He sees the lockdown as an opportunity to be whoever he wants.
Small tensions surface during cohabitation. Ciara notices missing asthma inhalers despite Oliver's claims, overhears a tense call in which someone accuses him of hiding things, and one night Oliver physically blocks her from leaving the apartment during a fire alarm. Outside, she encounters a journalist named Laura Mannix, who asks if Ciara is staying with "Ollie" and offers help.
A property manager reveals apartment one is a corporate let rented by KB Studios. Karl contacts the firm and learns their tenant was an "Oliver Kennedy," matching the body's description. When Lee finds a cream envelope in the letterbox addressed to "Oliver St Ledger," she connects the name to the Mill River case, a notorious 2003 murder in which two 12-year-old boys killed a 10-year-old named Paul Kelleher. Their identities were legally protected as Boy A and Boy B. Oliver received a lighter sentence; Shane, Boy A, later died by suicide. Lee and Karl agree to guard this information carefully.
A deeper flashback reveals Ciara's true identity. She meets her older sister Siobhán in Cork and learns their mother is entering hospice care. Shane, Boy A, was their brother. Their mother never recovered from the crime; their father died by suicide. Ciara wants to find Oliver and learn the truth for her mother's sake. She traces him through his brother Richard's social media to KB Studios, relocates to Dublin, and constructs an elaborate cover: a fake employer, a disposable phone, and a fabricated last name. She buys the Space Shuttle tote bag at a charity shop, knowing Oliver wore a NASA T-shirt the day of the murder. Her "chance" supermarket encounter is the result of five days of following him.
Back in the countdown, Ciara tells Oliver that Laura is a journalist who knows his real name. Cornered, Oliver confesses: In 2003, he and another boy named Shane killed Paul Kelleher. Shane began beating Paul; Oliver held Paul's arms; they drowned him in the river. Oliver insists he was a follower, not the instigator. Ciara packs and leaves. Her perspective reveals the agony beneath her reaction: she must conceal that Shane was her brother and that she already knows the story.
Oliver spirals, stops eating, and contemplates the Rohypnol pills before pulling back. Days later, Ciara returns to check on him and stays overnight while he takes a tranquilliser to sleep. After swallowing the pill, Oliver discovers a notebook in Ciara's bag containing research notes: Space Shuttle facts, cover-story dates, and a LinkedIn screenshot for a different woman. He realizes her identity is fabricated. As the drug takes hold, he stumbles into the bathroom, falls through the glass shower door, and hits his head. Ciara rushes in. In his final conscious moments, Oliver delivers a devastating revision: he was the ringleader, not the follower. Everything he attributed to Shane was his own doing. Shane attacked him in detention because Oliver refused to tell the truth; Shane died by suicide because no one believed him. Ciara screams and reveals her own secret: she is Shane's sister, Ciara Hogan.
Oliver loses consciousness. Water from the shower runs over his face.
The deputy state pathologist determines Oliver drowned in shower water while unconscious from the Rohypnol and notes the apartment has been wiped clean of fingerprints: "Why would someone wipe down an apartment after an accident? And why on earth didn't they call for help?" (334). CCTV footage shows Laura Mannix, the journalist, entered apartment one days after the death, contradicting her claims. Lee discovers Laura's presence in the building was arranged by the wife of KB Studios' managing director, who despised Oliver and leaked his whereabouts. The case is classified as accidental death, though Lee remains uneasy.
The epilogue, set three days later, confirms the truth. After Oliver's confession, Ciara stands over his unconscious body and watches water pool around his face. She turns off the shower when she first enters the bathroom; after hearing his confession, she turns it back on. She spends the night wiping every surface clean and sends a final text from her disposable phone to simulate a breakup. Her cover identity is so thorough she is effectively untraceable.
Walking Sandymount Strand, Ciara acknowledges she has done the very thing she feared her brother had done. There is a killer in her family, but it is her. Her phone rings: Siobhán tells her their mother is dying. Ciara asks to be put on speaker and, in what may be her mother's final moments, begins to tell her something about Shane, intending to clear his name at last.