including ourselves into the bargain, if he heard so much as a
whisper from us," added Kennedy firmly.

"That second person has left the storeroom, Craig," I put in. "The
buzzing has returned again full force."

Kennedy tore the wireless receiver from his ear. "Here, Walter,
never mind about that electric detective any more, then. Take the
optophone. Describe minutely to me just exactly what you hear."

He had taken from his pocket a small metal ball. I seized the
receiver from him and fitted it to my ear. It took me several
instants to accustom my ears to the new sounds, but they were
plain enough, and I shouted my impressions of their variations.
Kennedy was busy at the window over the heavy package, from which
he had torn the wrapping. His back was toward us, and we could not
see what he was doing.

A terrific din sounded in my ears, almost splitting my ear-drums.
It was as though I had been suddenly hurled into a magnified cave
of the winds and a cataract mightier than Niagara was thundering
at me. It was so painful that I cried out in surprise and
involuntarily dropped the receiver to the floor.

"It was the switching on of the full glare of the electric lights
in the art-gallery," Craig shouted. "The other person must have
got up to the room quicker than I expected. Here goes."

A loud explosion took place, apparently on the very window-sill of
our room. Almost at the same instant there was a crash of glass