Gwen Lytton locks her granddaughter Coco in the kitchen while playing mahjong. Coco suffers from gas poisoning and weakly contacts her mother, Joan Ring, via smartwatch. The call abruptly ends as the battery dies. Joan desperately tries calling her mother-in-law, but the phone rings unanswered amidst loud mahjong noises. Her husband, Leon Childe, dismisses her concerns while out with his first love. With time running out and no one to help, can Joan save Coco successfully?
