detector in
series, it is only a matter of applying an ordinary photo-recording
drum, and the machine is made."

He had been setting up a light-tight box, inside of which was a little
electric lamp. Opposite was a drum covered with bromide paper. He
started the clockwork going and after a few moments' careful
observation, we went away, and left the thing, trusting that no one was
the wiser.

Nothing further occurred that day, except for frequent reports from
Burke, who told us how his men were getting on in their shadowing of
Forsythe & Co. Apparently, the death of Leon had put a stop to
revolutionary plots, or at least had caused the plotters to change their
methods radically.

The time was shortening, too, during which Burke could keep the
passengers of the _Haytien_ under such close surveillance, and it was
finally decided that on the next morning they should be released, while
all those suspected were to be shadowed separately by Secret Service
agents, in the hope that once free they would commit some overt act that
might lead to a clew.

CHAPTER XXXIII

THE RESPIRATION CALORIMETER

It was early the next morning, about half an hour after the time set for
the release of the passengers, that our laboratory door was flung open
and Collette Aux Cayes rushed in, wildly excited.

"What's the matter?" asked Kennedy anxiously.

"Someone has been trying to keep me on the boat," she panted. "And all
the way over here a man has been following me."

Kennedy looked at her a minute calmly. We could understand why she might
have been shadowed, though it must have been a bungling job of Burke's
operative. But who could have wanted her kept on the boat?

"I don't know," she replied, in answer to Kennedy's question. "But
somehow I was the only one not told that we could go. And when I did go,
one of the Secret Service men stopped me."

"Are you sure it was a Secret Service man?"

"He said he was."

"Yes, but if he had been, he would not have done that, nor let you get
away, if he had. Can't you imagine anyone who might want you detained
longer?"

She looked at us, half frightened. "N--not unless it is that man--or the
woman with him," she replied, clasping her hands.

"You mean Castine?"

"Yes," she replied, avoiding the use of his name. "Ever since you had
the body removed, he has been in great fear. I have heard him ask fifty
times, 'Where have they taken him?' and 'Is he to be embalmed?'"

"That's s