The Unfriend

Peter and Debbie, a middle-class English couple celebrating twenty years of marriage on a cruise, strike up a holiday friendship with Elsa, an eccentric and outspoken American widow. They exchange contact details and assume they will never see her again, but Elsa unexpectedly invites herself to stay at their home. When Peter and Debbie look her up online, they discover unsettling evidence suggesting she may be responsible for the deaths of several family members.