As the title would suggest, this is a dated British murder mystery mostly set in and around an old dark house where amateur sleuth Pierre Santos (a stand in for Hercule Poirot if ever I saw one) must discover which one of the house guests has bumped off the aristocrat in whose home they are currently staying.
Before this set-up, we get a few police procedural type scenes of murders and the subsequent investigations involving old diary pages found at each crime scene, before things move towards an 'old dark house' style scenario. Sadly, during this era of British cinema, things were still very old-fashioned and stage bound, with heavily mannerismed acting and stilted dialogue. Not one drop of suspense can be wrung from the premise, leaving this an entirely ordinary movie.