Wedding of Will Slater and Julia "Jules" Keegan is taking place on the Folly, an island off the coast of West Ireland. As the guests celebrate, a storm approaches, causing the island's lights to go out, followed by a loud scream that alarms everyone.
The story then takes the reader back to the day before the wedding, introducing Aoife and Freddy, the new owners of the island. Aoife is the wedding planner, and Freddy assists her with the preparations. They are both anxious for the guests to arrive, hoping to attract more visitors and improve their business, as the island has been struggling to overcome the fear that the locals have of it.
As married couple Hannah and Charlie make their way to the island on a boat, the captain shares the haunting stories associated with the Folly. The island was once settled by a religious sect that mysteriously disappeared, only to be discovered later by archaeologists in a small enclosed pit on the island. This discovery has become a cautionary tale for the locals, warning them about the dangers lurking on the island, such as bogs, spirits, and caves.
Hannah, already feeling uneasy about the visit, becomes more unsettled after hearing the island's history. She is suspicious of her husband Charlie's close friendship with Jules, the bride-to-be. Hannah suspects that Charlie and Jules may have had a previous sexual relationship, which fuels her growing distrust in Charlie and her dislike for Jules. Charlie's behavior changes around Jules, as he puts on airs, changes his accent, and pretends to be as wealthy as Jules, Will, and their friends. Unlike the other guests, Charlie and Hannah have been facing financial difficulties, which adds to Hannah's feeling of inadequacy compared to Jules. Hannah also suspects that Charlie is jealous of Will.
Despite their relatively short relationship, Jules and Will are seen as a perfect couple. Jules is a successful magazine editor from a wealthy
family, while Will hosts a reality television show called "Survive the Night." They are considered a power couple. Jules and Will engage in public displays of affection and often film each other in nude scenes, enjoying the power dynamics of their relationship. However, Jules is concerned about their wedding day due to receiving an anonymous note warning her not to marry Will andnot to trust him three weeks earlier.
In the midst of trying on her wedding dress, Jules is interrupted by Will, who begins touching her. Their moment is further disrupted by Will's best man, Johnno, who confesses that he has forgotten to bring his suit. Will manages to find an extra suit for Johnno, but Jules doesn't like him and doesn't understand why Will remains friends with him. At some point, Will discovers that Piers Whiteley, the producer of his show, has been invited to the wedding. This revelation displeases Will, leaving Jules confused by his reaction. These events hint at the existence of secrets within their relationship.
Will's groomsmen arrive on the island. Duncan, Angus, Oluwafemi, and Peter are all from wealthy families and share a strong bond from their boarding school days with Will and Johnno. Johnno and Will have a closer bond than the others, as Johnno attended school on a scholarship, while Will's father was the headmaster. They were not as affluent as their classmates. The groomsmen, except for Johnno, have achieved great success in their respective careers. Duncan works in economics, Angus is involved in his father's firm, Oluwafemi is a surgeon, and Peter works in advertising.
Johnno, unlike the others, claims to have started a new whiskey business but it's later revealed to be a lie to cover up his lack of success. He had a friend create new labels and put them on cheap bottles of whisky from the store.
Upon Charlie and Hannah's arrival on the island, Jules takes Charlie away, leaving Hannah to seek solace in a cave. There, she encounters Olivia, Jules's 19-year-old half-sister and the maid of honor. Olivia struggles with mental health issues, self-harm, and an eating disorder. Her relationship with Jules is strained, with Jules being jealous of Olivia's perceived favored upbringing and feeling deprived by their mother, Araminta.
Returning to the night of the wedding, the waitress who screamed informs everyone that she has discovered a body. Aoife instructs the guests to stay inside for their safety. Will's groomsmen feel compelled to take action and discuss sending someone outside to investigate.
The face seen in the window is revealed to be Jules's father, Ronan. Jules has a contentious relationship with her father, and his presence at the wedding, along with his new wife Severine, adds to the awkwardness. During dinner, Jules observes the interactions between her friends and family, noting the underlying tension and exchanges of barbs.
Jules's mother, Araminta, stands to give a toast, which annoys Jules. Araminta praises Jules for her independence and takes credit for raising her to be strong, but Jules feels bothered by it. However, Will manages to lift her spirits by talking about how he had to persuade her to go on a date. Their affectionate moment is overshadowed by Jules's doubts caused by the anonymous warning letter she received.
The conversation shifts to a game called Survival that they used to play at boarding school, with the exception of Will. Duncan's wife, Georgina, makes a joke about the game not causing any deaths. Johnno reacts strongly to this comment, reminiscent of a traumatic experience in the woods where he was tied down. This foreshadows a key plot point in the novel. Hannah, a graphic designer on permanent maternity leave, admires the design of Johnno's whiskey logo.
Everyone drinks Johnno's whiskey, but some, including Jules, are not enthusiastic about its taste. Jules's mother leaves the table, and Hannah tries to persuade Charlie to leave as well, but Johnno and the other men pressure him to stay. It is revealed that the group had left Charlie stranded on a small island during the bachelor party. Hannah becomes increasingly unimpressed with Charlie's desire to fit in with the group.
The men stand up and start drumming on the table, chanting Latin refrains repeatedly. Hannah is frightened by their behavior, especially when they let out a roar and appear changed after the ritual. Only Johnno seems tobe faking his excitement. Angus explains that the Latin chant is a combination of their school's motto and their own creation.
They then engage in heavy drinking.
Hannah, irritated with Charlie, encounters Olivia in another room. To escape the noise, they take vodka and cigarettes to the cave. Olivia shares details of her breakup, including creating a fake dating profile and starting a relationship with an older man named Steven. However, Olivia ruined things by getting drunk at one of Jules's parties and acting immaturely. She recalls the abortion she had, causing her distress. Hannah prompts her to continue, but Olivia is unable to say more.
Olivia encounters Johnno, who tries to initiate a sexual encounter with her. She rejects him and leaves him alone, where he starts hearing ghostly voices. Johnno breaks down in tears and insists to the voice that he didn't mean for whatever happened to occur.
Inside, Jules and Charlie have a tense exchange where she accuses him of being jealous. Charlie denies it and claims to want Jules to be happy. Jules questions if Charlie wrote the anonymous note, leaving him confused. Later, Will and Jules find seaweed in their bed, which freaks out Jules. Will convinces her that it's just a practical joke played by the ushers. Outside, Aoife discovers Johnno in a slump, looking like he's seen a ghost.
Returning to the night of the wedding, Femi and three ushers form a search party, equipped with a first-aid kit, and venture out into the storm with a frenetic excitement to find the body.
Hannah calls her mother, expressing her protectiveness over her children and loved ones. The anniversary of her sister Alice's death brings a change in pace for Hannah and her family. Olivia reminds Hannah of Alice in her sadness, thinness, and fragility. After the call, Hannah continues walkingand gets stuck in a bog. She struggles but is unable to free herself. Duncan and Pete appear and laugh at her, but eventually help her out. Feeling uncomfortable around them, Hannah quickly returns to the hotel.
Meanwhile, Aoife is preparing for the wedding when Will approaches her and reveals finding seaweed in the bed. Aoife, concerned about the success of her hotel business, remains unmoved by Will's flirtations. She observes how Will uses his sexual prowess as a display of power and
dominance. Aoife senses darkness in Will, echoing the warning from the note Jules received.
On the morning of the wedding, Jules sees Olivia standing on the cliff's edge but chooses to focus on preparing for the ceremony rather than addressing her concern. Jules tears up the warning note and is determined to have a perfect wedding and marriage. Olivia watches the boats carrying the guests approach the island, feeling guilty and believing she is the evil presence on the island. She wants to talk to Hannah about her abortion but overhears Charlie and Hannah arguing instead.
At the docks, Aoife welcomes the guests and converses with Mattie, the boat captain, who points out approaching dark clouds signaling an incoming storm. On the wedding night, Pete, intoxicated and high, gets stuck in the bog and urges the group to return to the hotel. He mentions seeing bodies in the bog, causing the group to realize their vulnerability in the storm. Paranoia sets in as a figure approaches them in the darkness, revealed to be Freddy, Aoife's husband.
Johnno asked to be Will's best man due to the shared history and experiences they had at boarding school. Will got away with pranks and mischief because his father was the headmaster, and he was a bad student who still excelled in the GCSE exams. Johnno reminisces about a boy named Loner who used to follow Will around and often reported their tricks to the matron.
Before the ceremony, Will pulls Johnno aside and warns him not to embarrass him during the best man's speech. Jules, wearing a gold crown, confronts her father, Ronan, for the first time since he met Will. Ronan is unimpressed with Jules's fianc?, leading Jules to express her anger and disappointment at her father's absence in her life. She insists that he at least pretend to be happy for herand Will as he walks her down the aisle. Jules then breaks things in her room, a habit she has been fighting since being with Will, before composing herself and heading out with Ronan, Aoife, and Olivia for the ceremony, which goes smoothly.
Hannah closely watches Charlie during the ceremony, suspecting that
he may be jealous of Will. She has been preoccupied with thoughts about Charlie and Jules possibly having slept together, prompted by Johnno's comment the night before. After the ceremony, Hannah approaches Charlie and brings up the stag weekend, expressing her concern about his drinking. Charlie snaps at her, indicating a potential history of alcoholism. Meanwhile, Johnno has a confrontation with Will's father, the former headmaster, who accuses Johnno of stealing GCSE papers for Will's cheating. However, it is revealed that it was actually Will who stole the papers. This encounter, along with learning that Will intercepted an offer for Johnno to join the show, marks a betrayal that changes everything for Johnno.
As Will attempts to intervene in a conversation between Johnno and Piers, guests panic over Olivia, who has wandered into the sea and is drowning. Will saves Olivia, becoming the hero of the moment. Jules initially worries for her sister but quickly becomes angry, accusing Olivia of seeking attention and trying to upstage her. Hannah defends Olivia, suggesting that she may be struggling with mental health issues, but Jules dismisses her and shouts at Hannah as well. Aoife steps in and redirects the guests back to the marquee, where the party resumes.
Johnno is consumed by bitterness and fury as he watches Will emerge from the water as the hero who saved Olivia. Everything falls into place for Johnno, and he becomes determined to seek revenge on Will for the secrets he has kept for him.
Hannah, though realizing that Olivia is not her sister Alice, tries to comfort her. Olivia reveals that she was pregnant with Steven's child, but he abandoned her during the pregnancy and subsequent abortion. Hannah shares the story of her sister, Alice, who faced a similar situation. Alice was intelligent and aspired to work in politics, but explicit pornographic videos of her, published by her ex-boyfriend, destroyed her dreams. Olivia and Hannah bond over their shared experiences, and Hannah encourages Olivia to seek help from her family. However, Hannah doesn't have the chance to tell Olivia thatAlice eventually took her own life due to the shame and belief that her political aspirations were impossible.
In the kitchen, Aoife breaks down with Freddy, blaming herself for
Olivia's possible drowning. Aoife's breakdown ties together various threads introduced throughout the chapters, including her connection to the graveyard and Hannah's discovery of a grave belonging to a drowned child.
During Ronan's speech as the father of the bride, Jules grows increasingly angry as his sudden pride contradicts his previous financial cutoff. Without her father's support, Jules opted for the discounted wedding at the Folly. Ronan concludes his speech with a threat, warning Will to take care of Jules or face consequences. This contradictory display of recognition and pride moves Jules to tears.
Olivia's inner monologue reveals that Will and Steven are the same person. Will had threatened Olivia to keep her from telling Jules, fearing that she wouldn't believe her. Olivia wrote the anonymous note to warn Jules about Will. The tension builds as the novel heads towards its climactic point.
During his best man's speech, Johnno subtly threatens Will and reveals damaging information about both of them. It is revealed that Johnno couldn't afford the suit he was supposed to buy, and Will didn't offer to buy it for him. At the end of the speech, Johnno initiates an impromptu game of Survival, blindfolding Will. Meanwhile, on the night of the wedding, Freddy informs the group that the police have been called, and they head back to the hotel. The search party becomes chaotic and confused, realizing that they have lost Pete along the way.
The men leave Will blindfolded in a cave during the impromptu game of Survivor. Johnno stays behind and confronts Will about the television show and his whisky company. Johnno reveals that his whisky business is fake and expresses his deep hurt and anger over Will cutting him out of the television deal. The conversation turns to a haunting memory from their past - the death of a young boy named Loner during a game of Survival.
Back at the tent, Charlie gets into a fight with another partygoer, and Hannah intervenes. She confronts Charlie about what happened during the bachelor's party, and he drunkenly recounts how he was left alone on an island after consuming magic mushrooms. Charlie believes that
Will orchestrated the ordeal. Hannah also discovers that Charlie had slept with Jules,cheating on her while she was still recovering from giving birth and dealing with postnatal depression. She snaps at Charlie, refusing to clean up his messes and demanding that he pull himself together.
In the cave, Johnno and Will discuss the death of Loner. Loner had discovered that Will had stolen the answers to the GCSE exam, and Will wanted to eliminate him. Johnno and Will kidnapped Loner and tied him up on the beach, resulting in his drowning when the tide rose. Will's father intervened, and the incident was ruled as an accident. Johnno carries immense guilt over Loner's death and demands to know if Will planned it. Their conversation is interrupted by Aoife, leaving Johnno wondering what he would have done if no one else had witnessed their actions.
Jules is enraged and humiliated by Johnno's speech, but Will comforts her and promises to cut Johnno out of their lives. Meanwhile, Hannah storms off and dances with a man who knew Will from college. On the night of the wedding, the search party discovers a twisted golden crown on the ground.
Jules overhears a conversation between Olivia and Will, leading to her intense humiliation and anger. She rips off her crown and stomps on it, symbolizing her betrayal by Will. Jules then calls Will and Olivia back into the tent to cut the wedding cake, potentially saving Olivia from a dangerous situation. For the first time, the novel shifts to Will's perspective, revealing that he had considered getting rid of Olivia.
Later that night, the ushers discover a dead body, which turns out to be Will. The men are overcome with grief, crying loudly and feeling completely lost. The perspective in the novel rapidly changes between Hannah, Olivia, Jules, Johnno, Aoife, and Will as the lights go out. The two timelines of the novel, previously separate, have now converged.
The identity of Will's murderer is revealed. Despite the many possible
suspects, including Jules, Olivia, Hannah, and Johnno, it is actually Aoife who confronts Will in the dark after the lights go out. Aoife reveals that the young boy, Loner, who died years ago at boarding school was actually her brother named Darcey. Darcey had discovered that Will had stolen the GCSE papers and was killed as a result. Aoife and her husband, Freddy, planned the wedding on the Follyto confront Will and uncover the truth. After overhearing Will and Johnno discussing the matter, Aoife is certain of Will's guilt and takes revenge by stabbing him in the heart with a cake knife, killing him. She blames Will for the death of her brother and the subsequent loss of her parents, who died from the grief of losing Darcey.
In the present, the groomsmen mistakenly believe that Johnno is the murderer as he approaches them covered in blood. However, Johnno is innocent and only found Will's body and pulled out the knife. Once again, he is falsely accused, similar to the blame he received for the GCSE exam answers. Johnno, resigned to his fate, believes he will go to prison to atone for Darcey's death. The police arrive and take Johnno into custody.
Meanwhile, Olivia and Jules reconcile and begin to mend their relationship. Jules confesses that she knows what Will had done to Olivia, and instead of hating her, she breaks down in tears and embraces her, feeling like true sisters for the first time. Hannah and Charlie leave the island together, but their relationship has been irreversibly changed. The novel ends with Hannah wishing she had been the one to kill Will, highlighting the intense emotions and desire for justice that the events have evoked.