The cinematic journey unfolds in a bustling corporate environment where coworkers Charlie (Dan Stevens) and Mina (Sheila Vand) are excitedly scouring a listing for a weekend getaway. They are soon joined by Josh (Jeremy Allen White), Charlie's sibling turned romantic partner, whose infectious enthusiasm adds to the anticipation. At home, Charlie confides in his wife Michelle (Alison Brie) about Josh's troubled history, crediting Mina for helping him find his footing.
As the group heads out for their much-anticipated retreat, tension brews when Charlie expresses his frustration at Josh's insistence on bringing their beloved dog Reggie despite a strict no-pets rule imposed by the homeowner. Josh remains steadfast, choosing to sneak Reggie into the trip. The journey takes a thought-provoking turn as the couples engage in a revealing discussion about Mina's experience with racial bias; she had faced rejection for an application to the getaway house, only for Charlie to be accepted shortly thereafter.
Upon their arrival, they are greeted by the homeowner Taylor ([Toby Huss]), whose patronizing comments towards Mina raise eyebrows. During their property tour, she confronts him about her denied application, but he brushes off her concerns without offering any explanation. The group can't help but notice a mysterious locked door beneath the house, hinting at secrets lurking behind a façade.
As evening descends, Charlie and Mina take a contemplative walk along the beach, leaving Josh and Michelle behind for heartfelt conversation. Josh's insecurities bubble to the surface as he expresses worry about Mina's potential to outgrow him due to her close relationship with Charlie. While Michelle tries to reassure him, she too feels unsettled by the bond shared between her husband and Mina.
Returning to the home, the group finds an unexpected gesture from Taylor: a telescope to view the stars. However, Mina's intuition raises red flags, sensing that there may be more than meets the eye. The night spirals into unexpected territory when Michelle, trying to spark some fun, introduces drugs to the mix. Though exhaustion takes over, leaving Michelle unable to partake, Charlie, Josh, and Mina succumb to the allure of indulgence.
The trio's night takes a dramatic turn when the bliss of their escapades escalates into a moment of vulnerability. Charlie confesses how Mina has inspired him to strive for personal betterment, culminating in a passionate kiss and subsequent rendezvous in the shower. But as dawn breaks, guilt begins to set in for both Charlie and Mina.
Awakening with the fog of their revelry still lingering, Charlie and Mina find themselves unable to commence their planned hiking adventure. Josh and Michelle, however, venture out, leading Michelle to bring up Charlie's pre-marital fling with Jen. Josh admits he had his own dalliance with Zoe, adding to the undercurrents of tension within the group. Meanwhile, Charlie and Mina exchange glances, trying to downplay the significance of their previous encounters.
The atmosphere shifts dramatically when Michelle stumbles upon an ominous discovery: a camera lens seemingly protruding from the showerhead. Alarm bells ring as she confronts Charlie, and the pair fear their intimate moment may have been recorded. They realize that reporting it to authorities would betray Josh's trust, placing their fragile relationships in jeopardy. Upon returning home, Michelle probes Charlie about his past, his admissions only adding to the existing strain in their marriage.
In a bid to uplift spirits, Michelle resorts to increasing their drug use, while Josh grows frantic at the sudden absence of Reggie. Fearing the worst, he accuses Taylor of taking his dog, and the atmosphere becomes charged when Taylor is summoned to fix the hot tub. Tensions explode when Josh confronts Taylor, leading to chaos and misunderstandings.
As they grapple with the aftermath, the plot takes a sinister twist when Taylor is discovered dead, sending shockwaves through the group. Instead of reaching out for help, a misguided decision leads them to dump Taylor's body off a cliff, attempting to disguise his death as an accident.
Later, a masked figure appears, revealing their intent to exploit Charlie and Mina's affair by broadcasting their moments of intimacy, drawing Michelle into a tangled web of betrayal and violence. When chaos engulfs them, Michelle crashes her car while fleeing, and in a moment of desperation, Charlie races to help only to find his worst fears realized: her life has been brutally taken.
As the harrowing tale unfurls, Josh unwittingly finds himself enmeshed in the deceit, leading to his own demise at the hands of the same shadowy figure. In a frenzied finale, Mina's flight from the figure ends tragically as she tumbles off a cliff into the abyss.
The masked antagonist tidies up the scene, erasing all traces of the horrifying events that transpired. In a stunning conclusion, Reggie reappears, further emphasizing the darkness of the situation, while the narrative shifts to a new family moving into the now cursed apartment, blissfully unaware of the horrors that linger there. The film reaches its chilling end, leaving the audience with the chilling impression that danger can emerge in the most unexpected places.
