The Retreat

In the summer of 2003, teenagers Thea and Ollie sneak away from their camp on Cary Island. A dark, shapeless figure attacks Thea in the woods. Ollie witnesses the assault and, terrified, runs to hide in a cove. When he returns, he finds Thea motionless. He cannot bring himself to look closely at her body, but he discovers a large stone nearby, shaped to resemble the island's landmark, Reaper's Rock.

Years later, travel influencer Jo Leger arrives at LUMEN, a new luxury retreat on Cary Island, and posts a video detailing the island's grim history, including the 2003 murders attributed to caretaker Larson Creacher. Elsewhere, Detective Sergeant Elin Warner, on reassignment after a career break taken for anxiety, sees her colleague DC Steed at a beach where a body has been found. The incident triggers her anxiety, which is linked to her brother Sam's childhood death and a strained relationship with her father. Her boyfriend, Will, is the architect who designed LUMEN.

Hana Leger, Jo's sister, arrives for a family trip, still grieving the recent death of her partner, Liam. She is joined by her cousin Maya, Jo's boyfriend Seth Delaney, and Caleb, the boyfriend of their older sister Bea, who has canceled for a work trip. Hana finds a crumpled note from Jo's bag with the words "I'm sorry" written three times. On the boat to the island, Hana and Maya recall a childhood promise to "stick together" made after a house fire that severely injured Maya's younger sister, Sofia. Upon arrival, the group goes kayaking, and tensions surface during dinner that evening.

The next morning, a cleaner named Michael Zimmerman discovers a woman's body on the rocks below the yoga pavilion. Elin and Steed are dispatched to the island, where they are met by Will's sister, Farrah, a manager at the retreat. The victim, a fair-haired woman, appears to have died from a fall. CCTV footage confirms this, showing an intoxicated woman dropping her wrap over the glass balustrade and falling while trying to retrieve it. Hana, heading to breakfast, recognizes Jo's distinctive wrap in an evidence bag and sees the body. Just then, Jo returns from a run. Hana insists the victim is their sister, Bea. After Caleb confirms Bea canceled her US trip, Jo looks over the edge and confirms the body is indeed Bea's.

Elin begins her investigation. Jo admits to arguing with Bea, suggesting Bea came to the island as a surprise to make amends. A water sports instructor, Tom, reveals he was a friend of Bea's and secretly brought her to the island the previous night. He says she received an upsetting phone call before leaving him around 11:30 p.m. Elin finds Bea's suitcase, which is missing swimwear, and a planner containing website addresses for a financial crimes site and a local history site about the island. Hana tells Elin that Maya heard someone leave their shared villa around 12:15 a.m. the night Bea died. Elin decides to stay on the island and invites Will to join her. Before he arrives, he shows her a threatening tweet with her photo, its eyes scratched out. That night, Elin sees a hooded figure with a flashlight in the woods.

The following day, a guest is reported missing, along with diving equipment. Elin, Steed, and Tom take a boat out and discover a body in full diving gear wedged between underwater rocks. It is Seth Delaney. Tom reveals that Seth's wealthy father, Ronan Delaney, owns the island. He also notes that the air valve on Seth's cylinder was turned off and his hood looked as if it had been pulled. Elin and Steed find packages of drugs in a bag floating nearby and a powdery residue near Seth's mouth, concluding he was murdered. When they inform Jo, she reveals Seth had a past drug dealing conviction and had been receiving threatening emails, which makes her suspect Maya, who was angry with Seth for rescinding a job offer. A search of Seth's room uncovers hidden cash and a climbing carabiner.

The carabiner leads Elin to theorize that Seth, an experienced climber, murdered Bea. She discovers a climbing bolt on the cliff face below the yoga pavilion and a hidden bag of climbing gear. She deduces that Seth staged a fall to lure Bea to the edge and pulled her over. As she leaves the area, a large boulder falls from the cliff, narrowly missing her. Meanwhile, Caleb tells Hana he overheard Seth telling Jo she must confess to leaving the villa on the night of Bea's death. Hana then finds Bea's smashed phone hidden in Jo's room. The pathologist informs Elin that limestone powder was found in Bea's mouth, linking her to the island's quarry, and there were fingermarks on her arms.

Elin contacts retired DS Johnson, who worked the 2003 case. Johnson reveals he doubted Creacher's guilt, mentioning another girl, Lois Wade, who went missing from the island months before the murders. He also states that a teenage Farrah Riley was the key, but questionable, witness against Creacher. Maya reveals to Hana that Jo and Liam were having an affair. Hana confronts Jo, who confesses not only to the affair but also to being with Liam when he had his fatal cycling accident. She panicked and fled, telling no one. Jo also admits to meeting Bea on the island and later finding and hiding her smashed phone to conceal their communication. Enraged, Hana grabs Jo's wrist and squeezes it painfully. Shortly after, Farrah goes missing. Elin finds a smashed radio and a threatening message on Farrah's laptop: "I KNOW WHAT YOU DID. I KNOW THAT YOU LIED." Elin confronts Will, who confesses that he was "Ollie" from the prologue and that Farrah lied in her 2003 testimony to protect him. In a quarry cave, Elin and Steed discover a shrine with photos of the 2003 victims, Lois Wade, Bea, and Seth, each with a reaper-shaped stone beneath it. As a storm hits, Elin locks down the retreat.

The next day, Ronan Delaney arrives. Elin identifies Caleb from a 2003 group photo as a camp leader named Christopher Jackson, the son of the 2003 boatman, Porter Jackson. Caleb is missing from the lockdown. His real passport and Bea's phone are found planted in Hana's suitcase. The phone contains messages showing Bea had discovered Caleb's true identity and was confronting him about it. Elin deduces Caleb's motive is revenge on Ronan for a fraudulent investment that ruined his father, leading to his suicide. Caleb killed Seth and Bea to get to Ronan, using the island's "reaper" mythology as a misdirection. Elin goes to the private islet, where she finds Farrah alive but attacked. Caleb ambushes Elin, beats her, and destroys the bridge to the islet before fleeing. Elin swims back to the main island and hears a gunshot. Caleb has taken Ronan hostage. Elin confronts Caleb on Reaper's Rock, where he confesses to killing Bea and Seth but denies killing Jo. He shoots Ronan in the leg and Elin in the arm. As he prepares to kill Elin, she and the newly arrived Steed overpower him.

In the hospital, Elin learns Caleb confessed to murdering Bea and Seth, and that his father, Porter Jackson, is now believed to be the real 2003 killer. Jo's murder remains officially unsolved, as Caleb denies involvement. After her visitors leave, Elin receives another tweet, this one containing a photo of her in her hospital bed, proving her stalker is still at large. Two weeks later, a flashback reveals Maya killed Jo on the beach with a rock. Her motive was revenge for Jo having started the childhood house fire that caused her sister Sofia's permanent brain damage.