midnight
If Manderson was in the house that night , and if he did not leave it until some time after 12.30 , Marlowe could not by any possibility have had a direct hand in the murder . It is a question of the distance between Marlstone and Southampton . If he had left Marlstone in the car at the hour when he is supposed to have done so -- between 10 and 10.30 -- with a message from Manderson , the run would be quite an easy one to do in the time . But it would be physically impossible for the car -- a 15 h.p. four-cylinder Northumberland , an average medium-power car -- to get to Southampton by half-past six unless it left Marlstone by midnight at latest . Motorists who will examine the road-map and make the calculations required , as I did in Manderson 's library that day , will agree that on the facts as they appeared there was absolutely no case against Marlowe . But even if they were not as they appeared ; if Manderson was dead by eleven o'clock , and if at about that time Marlowe impersonated him at White Gables ; if Marlowe retired to Manderson 's bedroom -- how can all this be reconciled with his appearance next morning at Southampton ? He had to get out of the house , unseen and unheard , and away in the car by midnight .