Cordelia (2019)

Cordelia is a troubled, damaged soul who is only just recovering after some unnamed trauma; she is an actor rehearsing a play and comes to stay in a creepy London mansion flat occupied by her twin sister Caroline and Caroline's boyfriend Matt. When they leave her alone there Cordelia strikes up a friendship with Frank the charming, but strange and unreliable young man they can hear practicing his cello in the upstairs flat - a relationship which quickly becomes very disturbing.