Watch full movie online. Based on a true story, 3 Sleeps features 9-year-old Casey, who lives on a tough London estate with her mother and two young sisters. Casey is sworn to secrecy when her mother leaves the girls home alone for the weekend, but navigating an adult world alone won’t be easy. Things take a turn for the worse when Casey’s youngest sister falls seriously ill, leaving her caught between protecting her mum or saving her sister’s life.