. But weather conditions favored him; there wasn't a
breath of wind. And that he succeeded is proved by the fact that at
the present moment your room below is probably still full of poison
gas! Of course, it _may_ not have been a gas-shell; he may have
relied, as well he might do, on the burst! But I'm taking no chances.
You can well imagine that failing a knowledge of the arrangement on
the tower, no explanation of the mystery would ever have been found! A
thunder-bolt would be the popular theory, and if any fragments of
shell were found who would ever know from where it had been fired?"

"Gatton," I said, "I owe you my life. But why did this fiend try to
murder me?"

Gatton smiled.

"I have a theory, Mr. Addison," he replied, "and it is this: I believe
he thought that the indiscretion of a certain mysterious lady would
bring about his ruin. If I am not mistaken, she has already gone far
to put his neck in a halter; and he was determined to nip this latest
adventure in the bud by removing the object of her--"

I felt myself changing color, and:

"For heaven's sake say no more!" I interrupted. "It is a gruesome and
horrible thought! Yet, perhaps you are right. What must we do, Gatton?
These people have rendered the neighborhood uninhabitable for
themselves, now, and--"

Dimly to my ears came the sound of a gun-shot.

"And have fled!" cried Gatton, springing up. "Quick! we must chance
the gas!"

"Why? What was that shot?"

"A signal! Dr. Damar Greefe and 'the cat' have escaped!"

He raced out across the landing, amid a chorus of frightened inquiries
from the inn staff. I followed him into a front room, and:

"This comes of turning my attention elsewhere for half an hour!" he
cried angrily. "I seem to be cursed with fools for assistants!"

Throwing up the window, he leaned out. I stood at his elbow; and as I
looked I saw a great red glow rising from the distant woods. The sound
of a car approaching at headlong speed reached my ears, and at the
same moment I saw the headlights.

"Hullo, there!" cried Gatton. "Blythe! Petersham!"

The car stopped, and a cry came back:

"We've lost him, sir!... and the Bell House is in flames!"

CHAPTER XXI

IN LONDON AGAIN

"Then the sudden change in the police attitude towards Eric," said
Isobel, "is not due to any discoveries which you or Inspector Gatton
have made at Friar's Park?"

"That I cannot say," I replied. "We have made certain discoveries as I
h