t I didn't like to do it without your
sanction."

"It might have been a good idea, but on the whole it's probably better
that you didn't. Carnes, we'll go down to the water front and see
whether anything shows up to-night. High tide will be about
eleven-thirty. It's about half-past nine now. We'd better get going."

* * * * *

On the second drive to Michaelville, the fog patches were quite
noticeably denser than they had been earlier in the evening. Three
times the car had to pass through bands of fog which covered the road.
As they passed the second one Carnes suddenly began to cough.

"What's the matter, old man?" cried Dr. Bird, a note of anxiety in his
voice. For a few moments Carnes could not answer for coughing. He
seized the mask to tear it from his head but Dr. Bird restrained him.
In a few minutes his voice became intelligible.

"It seemed like that fog bit right into my lungs, Doctor," he gasped.
"I felt as if I were choking. It's better now."

"Are you sure your mask isn't leaking, Carnes? It'll be all up with
you if it does. Test it."

The detective closed the intake valve of the mask and expelling all of
the air from his lungs, took a deep breath. The air whistled noisily
in through the outlet valve.

"The devil!" cried the doctor. "Take that mask off and let me look at
it."

A few moments were enough to make the needed repairs and they drove
on. Carnes still coughed from time to time. At Michaelville, they
started the scooter and ran down the track to the river. They secreted
the scooter under the parapet on the water pent-house and walked to
the river's edge.

"There's no telling just where they may land, Carnes," said the doctor
reflectively, "but this looks like the most likely place. I'll tell
you what we'll do. The river narrows a good deal about half a mile
east of here. You go up to the narrows and keep watch while I stay
here. If any craft passes you, follow it upstream until you find me.
If they land, handle the situation as well as you can alone. If you
hear any shooting, come as fast as you can leg it. I'll do the same."

* * * * *

The detective stole away into the darkness and Dr. Bird settled
himself for a long vigil. For an hour nothing broke the stillness of
the night. Suddenly the doctor was on his feet, peering downstream. A
faint purring murmur came over the water, so faint that no one with
less sensitive ears