--and he was willing to risk
death in the sink-hole sooner than let it go? Likely he meant to tear my
hands from the plank but hang on to it himself. Of course it got away
from us both. That's the whole story. Your own wonderful endurance and
mastery of swimming saved me. Doesn't that seem to clear up everything?"

"Almost everything. Yet I don't see why Dell waited--why he hadn't got
the treasure out some time night before last--or yesterday----"

"Of course he couldn't work in daylight. Most of the night after his
disappearance the lagoon was guarded. Yet it isn't easy to see why he
didn't make the attempt the night of his disappearance----"

"I suppose he was waiting for a favorable time. He had to have certain
equipment, I suppose--to keep from being carried down. Perhaps there are
certain periods when the flow through the channel is less, and there
isn't so much suction----"

A sudden light in the girl's face arrested me and held me. Her eyes were
sparkling like blue seas in the sunlight. "'At F. T.,'" she quoted.
"Ned, Ned, what stupids we are! Don't you see----"

"I can't say that I do. I saw 'At F. T.,' at the bottom of the script,
but I don't know what it meant----"

"'At flood tide'--that's what it meant! Just as a sailor would say it.
He told on his own directions the way to safety. When the tide flows
the water movement is probably in the other direction through the
underground channel, and the lagoon is as safe as a lake; and it's only
in the ebb-tide that the suction exists. And of course the ignorant
treasure-seeker would make his search in the ebb-tide, when the surface
of the lagoon is still."

Exultant over this, a discovery that, if the treasure was a reality,
assured its procurance, neither of us noticed the dignified, courteous
approach of Pescini from the hallway. He was distinguished as ever, his
dinner-jacket unruffled, his linen gleaming white in the dying light.

"Have you seen Sheriff Slatterly anywhere?" he asked me. "I'm in a sort
of quandary--I've got a letter on my hands and don't know what to do
with it."

"A letter?" I repeated. The skin was twitching on my back.

"Yes. I hardly know whether to send it on--or whether he will want it
for the investigations. It's one that Major Dell gave me a few days ago
to mail, but which I dropped in my pocket and forgot."

CHAPTER XXVI

The guests refused to go back to their city homes until they had seen
the contents of the chest