he hook."

"It's a howler, all right, Chief!"

"Oftentimes a book or magazine gets under a receiver and lifts it up an
inch or more. This attracts the attention of the central operator who
thinks somebody is trying to get a number. When the situation is clear
to her that the receiver is off the hook, or that the circuit is closed
without anybody being at the receiver end, she notifies the
wire-captain or chief-operator. It was either one or the other who put
the howler on after Stockbridge was shot and the 'phone had fallen to
the floor. Is that satisfactory? Does that explain the noise we heard
in the library before we broke down the door?"

"I see now, Chief. I thought all along it was spirits like the rest of
the job. Outside of spirits, what is the answer to the things that
happened in that house? I know it. I deduct it, Chief. The old man was
expecting somebody all of the time. He let this somebody into the
library when the butler wasn't looking. Maybe it was a woman, for all
we know. Maybe a German spy. Maybe anybody. This somebody got in an
argument with him over spoils on some deal, and shot him dead. That's
my idea, Chief!"

"You've missed your profession, Delaney. You've disgraced the firm! How
did the library door get locked on the inside? How did that happen? Did
Stockbridge, shot through the brain, rise and do it? It was mighty well
locked--you remember!"

"I never thought of that," admitted the operative. "Then it looks,
Chief, as if it was a case of suicide."

"Fosdick said the same thing without having many facts. How could a
right-handed man shoot himself behind the left ear? How could he do a
thing like that and then get rid of the weapon without leaving a trace
of it? How--oh, well, get facts and you won't ask such questions!"

"Then it was done by an outsider?" blurted Delaney, staring through the
wind-blown snow which came off the housetops. "It was done by the
fellow who 'phoned and wrote that letter, or had the letter written? I
don't see how he could do it!"

Drew smiled at Delaney's candor. "Neither do I," he said simply. "But
we've crossed Forty-second Street and we're on the trail by everyday,
up-to-date methods which never fail if they are continued long enough
and men work hard enough. We'll start with Harry Nichols--the man in
olive-drab! I've his address!"

CHAPTER SEVEN

"THE SPOT OF BLACK"

Delaney stepped behind his chief and followed in single file as the
detecti