Now let us consider the alibi. 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
