The Eleventh Hour Guest (1945)

A scientist invents a sensational machine which can read the mind.He's invited his family plus an unexpected mysterious guest .The inventor has his guests' thoughts recorded unbeknownst to them and he tells them he'll read them tomorrow.As the guests do not really wish him well,there's a storm brewing.During the night ,the professor is poisoned and ,in the grand tradition of Agatha Christie ,everyone had a reason to get away with him.The intruder guest claims he is a detective and he investigates.But he might be an impostor.