As their parents head out for a date in the city, the three young Thompson children immediately take to their new babysitter Anna, who seems like a dream come true: she's sweet, fun, and lets them do things that break all of their parents' rules. But as Anna's interactions with them take on a more sinister tone, the kids realize that their caretaker may not be who she claims to be, and soon it's up to big brother Jacob to protect his siblings from the increasingly nefarious intentions of a very disturbed woman.