ecessary, while his right hand rested on the
butt of the revolver in his hip pocket.

At that moment there was a quite audible sound outside the door.
Morgan leaped forward and threw the door open. With the sound of the
opening door both men heard somebody break into a hasty descent of
the stairs. Morgan dashed through the door and down the stairs.
Tierney followed close behind him. Before they reached the front
door they heard the roar of an opened muffler and an accelerated
engine, and by the time they reached the front steps there was
nothing to be seen except the black shadow of an automobile without
lights rapidly disappearing down Sheffield Avenue.

"Well, I'm damned!" growled Tierney, as the car disappeared.

Morgan said nothing, but stood thoughtfully gazing down the street.

"What do you make of it?" inquired Tierney.

"Let's go up again," suggested Morgan, without replying to the
question.

Back in the living room, the men resumed their seats, and spoke in
lowered voices.

"It's hard to tell what it means," Morgan at last replied. "That's
the first time anything of the kind ever happened to me."

"How did you get wise?" asked Tierney.

"I heard the door move several times," Morgan explained. "At first I
thought it was the wind, but the last time I heard it I was sure it
had a different sound. It seemed to me that somebody had leaned
against the door while trying to listen."

"By God!" exclaimed Tierney. "This is SOME case, Morgan. Are we
spying on somebody, or is somebody spying on us? Marsh trails a
girl; I chase up Marsh; and now I'm damned if I don't think
somebody's chasing me, too."

"It begins to look like a bigger case than I thought, Tierney. An
ordinary murderer usually gets out of town or lays low. Quite likely
somebody is afraid we will unearth more than a murder. You run along
now. I want to be alone to think things over. On your way home stop
off and look up Murphy. Find out whether or not Marsh has left the
house tonight. Telephone me what you find out."

"Sure thing," answered Tierney, and picking up his hat, hurried
away.

Morgan sat down in his chair and began to refill his pipe. After
lighting it, he settled back into his chair and meditated on the
case. Reviewing in his mind the various bits of fact, information
and incident which he now had at hand, he endeavored to separate or
combine them according to their direct bearing upon the case.

In his earlier days Morgan had l