Surgeon Steven Murphy (Colin Farrell) befriends a 16-year-old boy named Martin (Barry Keoghan), following Martin’s father’s death on the operating table. After a time, Martin becomes closer to Steven and his family — including his wife, Anna (Nicole Kidman); his teen daughter, Kim (Raffey Cassidy); and his young son, Bob (Sunny Suljic). Martin even invites Steven to his own home for dinner, where Martin’s mother (Alicia Silverstone) flirts openly with the happily married Steven. Then one morning, Bob’s legs go numb, and he’s unable to walk and unwilling to eat. Martin visits again and explains that Bob’s condition will worsen — and the rest of his family will follow — unless Steven makes a terrible sacrifice.