“This is where he began to run. See how the pace shortens beyond this.”
Rather to the surprise of his companions, he continued to follow the trail.
“Is it really necessary to go as far as this?” Wendover demanded after a time. “You've come the best part of three-quarters of a mile from the rock. What are you trying to do?”
“I'm trying to find out the earliest moment when Billingford could have reached the rock, of course,” sir Clinton explained, with a trace of irritation.
A few yards farther on, Billingford's track was neatly interrupted. For twenty feet or so there were no tracks on the sand; then the footprints reappeared, sharply defined as before. At the sight of the gap Sir Clinton's face brightened.
“I want something solid here,” he said. “Stakes would be best, but we haven't any. A couple of cairns will have to do. Bring the biggest stones you can lift; there are lots up yonder above the tide-mark.”
He set them an example, and soon they had collected a fair number of heavy stones. Sir Clinton, with an anxious eye on the tide, built up a strong cairn alongside the last of Billingford's footprints which was visible.
“Now the same thing on the other side of the gap,” the chief constable directed.
Wendover suppressed his curiosity until the work in hand was over; but as soon as the second cairn had been erected at the point where Billingford's footprints reappeared on the sand he demanded an explanation.
“I'm trying to estimate when Billingford passed that point last night,” Sir Clinton answered. “No, I haven't time to explain all about it just now, squire. We're too busy. Ask me again in twelve hours or so, and I'll tell you the answer to the sum. It may be of importance or it mayn't; I don't know yet.”