Ready Or Not (2019 Film) - Wikipedia

As a child, Daniel Le Domas is confronted in his family's mansion by Charles, a wounded man who begs him for help. Instead, Daniel alerts his family, who arrive in ceremonial masks and robes. Despite his bride Helene's pleas, Charles is shot with a speargun and dragged away into a locked room.

Thirty years later, Daniel's brother Alex, the estranged son of the owners of the successful Le Domas Family Games company, is set to marry Grace, a former foster child. On Alex and Grace's wedding day, she meets the Le Domases: Daniel and his wife Charity; Alex's cocaine-addicted sister Emilie, her husband Fitch, and their young sons Georgie and Gabe; Alex's Aunt Helene, and his parents Tony and Becky. After the ceremony, Tony explains that his great-grandfather Victor Le Domas made a deal with someone named "le Bail" to build the Le Domas fortune in exchange for the family observing a tradition: at midnight on their wedding day every new member draws a game card from Le Bail's puzzle box. Grace draws "Hide-and-Seek". Believing it to be a harmless game, Grace hides herself as the Le Domases each receives a weapon. Alex finds Grace, who witnesses Emilie accidentally kill a maid whom she mistakes for Grace.

Alex reveals that his family is cursed: if the new member draws the Hide-and-Seek card, the rest must find and ritually sacrifice them before dawn, or they die instead. The card was last drawn by Helene's husband, Charles, who was then found and murdered. With the mansion locked down, Alex disables the security system to allow Grace to escape. She is discovered by Daniel, who is disillusioned with his family, and gives her a head start before alerting the others; Emilie accidentally kills another maid in the chaos. Grace's escape is blocked by the family butler, Stevens. She, in turn, splatters the freshly boiled tea he was preparing on his face and runs away. Daniel and Tony restrain Alex after he attacks the latter. Grace is seen by a third maid who accidentally crushes herself in a dumbwaiter while alerting the family to Grace's presence.

Grace runs to the goat shed, where Georgie shoots her in the hand. She knocks him out but is startled by a goat and falls into a pit filled with the remains of the Le Domases' previous sacrifices, including that of Charles. She escapes and makes it through the front gate. Grace is pursued into the forest by Stevens. She fights Stevens off but is eventually captured by him. As he is driving Grace back to the house, she awakens and attacks Stevens, causing the car to crash and killing him. Near the crash, Daniel captures Grace after realizing that his father is secretly watching.

The Le Domases prepare to complete the ritual sacrifice. However, they are incapacitated after Daniel poisons them with a non-lethal dose of hydrochloric acid in the ritual cup. Charity shoots Daniel in the neck after he attempts to protect Grace, leaving him to bleed to death as Grace runs away. In the ongoing chaos, the mansion is set on fire, and Grace is attacked by Becky, whom she beats to death with Le Bail's box.

Alex escapes his restraints and goes to find Grace, but witnesses her attacking his mother. Grace pulls away from Alex, who, after realizing that she will never trust him and will almost certainly leave him once she escapes, subdues her to complete the ritual. Grace breaks free from the ritual table just as the Sun rises. Despite Grace winning the game, Helene attempts to attack her, but explodes midstride as a result of the curse. The remaining members of the family explode one by one, leaving only Alex, who tries to convince Grace to forgive him. She refuses and tosses her ring back, declaring she wants a divorce; Alex then succumbs to the curse and explodes. Le Bail briefly shows himself to Grace and nods at her.

The sole survivor of the night, a blood-covered Grace, walks out of the burning manor just as the police arrive. Upon being asked what has happened to her, she replies, "In-laws."