The movie begins with Malorie Hayes (Sandra Bullock) urging two children, referred to as Boy (Julian Edwards) and Girl (Vivien Lyra Blair), to keep their blindfolds on during a perilous journey across a river. She clutches a box containing her pet birds, guiding the children along a string trail before they board the boat and set off.
Five years prior, Malorie, an artist expecting a baby, is visited by her sister Jessica (Sarah Paulson). Together, they watch a news report regarding mysterious mass suicides beginning in Siberia and spreading through Europe. Jessica observes that Malorie's painting reflects a lack of connection, reassuring her that it won't be so with her child. She accompanies Malorie to a prenatal appointment where their world begins to unravel. Upon leaving, they encounter a woman displaying alarming behavior and, as they realize the danger has reached America, chaos ensues. During their frantic escape, Jessica's demeanor alters, leading to a tragic accident that claims her life.
Amidst rising panic, Malorie is helped by a stranger, Tom (Trevante Rhodes), as they find temporary shelter in a house with other survivors, including Douglas (John Malkovich), a skeptical husband, and Lydia (Rebecca Pidgeon). They are introduced to a grim reality: a mysterious, unseen force that compels those who gaze upon it to take their own lives. As Malorie recounts the tragic events to Tom, the group fortifies the house against the outside world.
In the current timeline, after hours on the river, Malorie battles the darkness while trying to reach safety. Her attempts to communicate via radio lead to eerie encounters with the entity calling her name. Flashing back to the past, the group struggles for survival under mounting fears and dwindling supplies. They face internal threats, including the troubling influence of Gary (Tom Hollander), a man pushing the boundaries of sanity who seeks to unveil the entity—at devastating costs.
As their plight intensifies, Malorie and fellow survivors make desperate decisions, leading to heart-wrenching losses. Olympia ([Danielle Macdonald]), another pregnant survivor, seeks Malorie's support in a moment of vulnerability, solidifying an emotional bond between them that resonates throughout their harrowing journey.
Fast forward to 38 hours on the river. Malorie prepares the children for the approaching rapids, determined to navigate without anyone peeking. In the chaos of the past, the women enter labor, and while the world crumbles around them, fleeting moments of hope and connection emerge.
As they brave the perilous waters, tragedy strikes again when voices entice the children to remove their blindfolds. Malorie, embracing her protective instincts, fights through. The threat of the entity looms larger than ever as they inch closer to supposed safety, leading them to a sanctuary.
After an emotional journey filled with hardship, sacrifice, and resilience, they finally reach a compound that serves as a refuge, where Malorie reunites with Dr. Lapham (Parminder Nagra). Amidst the embrace of newfound security, Malorie names her children, reclaiming her identity as a mother. In a poignant act of freedom, she releases her birds into the sanctuary, symbolizing hope and a new beginning for their family amid the shadows of their past.
