Theydon was carried away in spite of himself.

“You believe that the airship might develop along the unemotional lines of the parcel post?” he inquired.

Forbes laughed.

“Exactly,” he said.  “I like your simile.  No one suggests that we Britons should endeavor to destroy our hated rivals by sending bombs through the mails.  Why, then, in the name of common sense, should the first—­ I might almost say the only use of which the airship is commonly supposed capable—­ be that of destruction?  Don’t you see the instant result of a war-limiting ordinance of the kind I advocate?  Suppose the peoples and the rulers declared in their wisdom that soldiers and war material should be contraband of the air—­ and suppose that airships do become vehicles of practical utility—­ what a farce would soon be all the grim fortresses, the guns, the giant steel structures now designed as floating hells!  Humanity has yet time to declare that the flying machine shall be as harmless and serviceable as the penny post.  I believe it can be done.  Come now, Mr. Theydon, I think you’ve caught on to my scheme—­ will you help?”

Help!  Here was a man expounding a new evangel, which might, indeed, be visionary and impracticable, but was none the less essentially noble and Christian in spirit, yet Theydon was debating whether or not he should give testimony which would bring to that very room a couple of detectives whose first questions would make clear to Forbes that he was suspected of blood-guiltiness!

The notion was so utterly repellent that Theydon sighed deeply; his host not unnaturally looked surprised.

“Of course, such a revolutionary idea strikes you as outside the pale of common sense,” he began, but the younger man stayed him with a gesture.  Here was an opportunity that must not be allowed to pass.  No matter what the cost—­ if he never saw Evelyn Forbes or her father again—­ he must dispel the waking nightmare which held him in such an abnormal condition of uncertainty and foreboding.

“Now that your daughter is gone I may venture to speak plainly,” he said.  “I told you that, I felt the need of a brandy and soda at Waterloo.  As a matter of fact, I did not leave the Brooklands track until six o’clock, and, as Innesmore Mansions, where I live, lie north, and I was due here at 7:30, I had my man meet me at the station with a suitcase, meaning to change my clothes in the dressing room there, and come straight here.  Guess my astonishment when I found Bates—­ Bates is the name of my factotum—­ in the company of two strangers, whom he introduced as representing the Criminal Investigation Department.”

He paused.  He had brought in his own address skilfully enough, and kept his voice sufficiently under control that no tremor betrayed a knowledge of Forbes’s vital interest in any mention of that one block of flats among the multitude.

Now, for the first time, Innesmore Mansions figured as his abode, the correspondence which led to the dinner having centered in his club.  But not a flicker of eyelid nor twitch of mobile lips showed the slightest concern on Forbes’s part.  Rather did he display at once a well-bred astonishment on hearing Theydon’s concluding words.