“Mrs. Lester wrote to an aunt in Oxfordshire, a lady who lives in the village of Iffley, near the first lock on the Thames below Oxford.  As it happened, this aunt, a Miss Beale, was lunching with a friend in Oxford today, and some one showed her an early edition of a London evening newspaper containing an account of the murder.  Instead of yielding to hysteria, and passing from one fainting fit into another, Miss Beale had the rare good sense to go straight to the police station.  One of our men has interviewed her this evening, and she is coming here tomorrow, but in the meantime the Oxford police telephoned the gist of the letter, which is headed ‘Monday, 11:30 p. m.’  The hour is not quite accurate, but near enough, since the context shows that a ‘friend’ had just called and given certain information which had determined the writer to leave London ’to-morrow’—­ meaning today—­ ‘or Wednesday at latest.’  So you see, Mr. Theydon, if the unknown is an honest man, he will soon hear of the hue and cry raised by the murder, and declare himself to the police.  Indeed, for all I know, he may have reported himself to the Yard already.  In that event you will probably meet him again quite soon.”

An electric bell jarred at the end of the main passage.  It smote on their ears with the loud emphasis of a pistol shot.  Even the detectives were startled, and Winter said, in a tone of distinct annoyance: 

“Go and see who the deuce that is, Furneaux.”

Furneaux returned promptly with Bates, pallid and apologetic.

“Beg pardon, sir,” said the intruder, addressing Theydon, but allowing his eyes to roam furtively about the room as though he expected to see something ghoul-like and sinister, “Mr. Forbes has rung up—­”

Theydon’s voice literally quavered.  For the first time in his life he knew why a woman shrieks in the stress of sudden excitement.

“Tell Mr. Forbes I am still engaged with the gentlemen from Scotland Yard,” he gasped.  “I’ll give him a call the moment I’m free.  He will understand.  Anyhow, I can’t explain further now.”

“Yes, sir,” and Bates disappeared.

“Mr. Forbes?  The gentleman you were dining with?” inquired Winter.

“Yes,” said Theydon.  He knew he ought to add something by way of explanation, but his heart was thumping madly, and he dared not trust his voice.

“You told him, I suppose, that Scotland Yard was worrying you, and he wants to know the result?”

Then Theydon saw an avenue of escape, and took it eagerly.

“I spoke of the murder, of course,” he said, “but Mr. Forbes was hardly interested.  He had seen the newspaper placards, and that was all he knew of it.  The truth is, he is wholly wrapped up in a scheme for reforming mankind by excluding airships and aeroplanes from warlike operations, and found me a somewhat preoccupied listener.  He wants my help, such as it is, and I have no doubt the present call is a preliminary to another meeting tomorrow.”