"Of course. But every season ticket-holder carries a key. This accounts for the guard not seeing him, and for the absence of a ticket. Now let me give you some information about the influenza. The patient's temperature rises several degrees above normal, and he has a fever. When the malady has run its course, the temperature falls to three- quarters of a degree below normal. These, facts are unknown to you, I imagine, because you are a doctor." I admitted such was the case. "Well, the consequence of this fall in temperature is that the convalescent's mind turns toward thoughts of suicide. Then is the time he should be watched by his friends. Then was the time Mr. Barrie Kipson's friends did _not_ watch him. You remember the 21st, of course. No? It was a most depressing day. Fog all around and mud under foot. Very good. He resolves on suicide. He wishes to be unidentified, if possible but forgets his season ticket. My experience is that a man about to commit a crime always forgets something." "But how do you account for the disappearance of the money?" "The money has nothing to do with the matter. If he was a deep man, and knew the stupidness of Scotland Yard, he probably sent the notes to an enemy. If not, they may have been given to a friend. Nothing is more calculated to prepare the mind for self-destruction than the prospect of a night ride on the Scotch Express, and the view from the windows of the train as it passes through the northern part of London is particularly conducive to thoughts of annihilation." "What became of the weapon?" "That is just the point on which I wish to satisfy myself. Excuse me for a moment." Mr. Sherlaw Kombs drew down the window on the right hand side, and examined the top of the casing minutely with a magnifying glass. Presently he heaved a sigh of relief, and drew up the sash. "Just as I expected," he remarked, speaking more to himself than to me. "There is a slight dent on the top of the window-frame. It is of such a nature as to be made only by the trigger of a pistol falling from the nerveless hand of a suicide. He intended to throw the weapon far out of the window, but had not the strength. It might have fallen into the carriage. As a matter of fact, it bounced away from the line and lies among the grass about ten feet six inches from the outside rail. The only question that now remains is where the deed was committed, and the exact present position of the pistol reckoned in miles from London, but that, fortunately, is too simple to even need explanation." "Great heavens, Sherlaw!" I cried. "How can you call that simple? It seems to me impossible to compute." We were now flying over Northern London, and the great detective leaned back with every sign of _ennui_, closing his eyes. At last he spoke wearily: