"One moment," protested Vernon. "We saw von Ruhle heave something over the quay. It might float; if so, there might be a chance to pick it up by means of a boat. The tide is almost slack. If it has sunk it will be a diver's task to recover it."
"'Something' is always unsatisfactory," remarked Ferret reprovingly. "Was it large, small, heavy, or light?"
"He was so jolly quick that I could hardly see it," replied Haye. "I should think it was about the size of a cigar-case."
Directing two policemen to remove and take charge of the body, the Detective-inspector accompanied the lads to the edge of the quay. It was dead low water. There was hardly sufficient current coming down the Stour to swing the anchored craft against the wind. Then the investigators made a discovery. Although there was a good depth of water at the greater extent of the quay, at this spot the mud was uncovered at the base of the wall, while almost at their feet was a flight of stone steps.
Ferret descended cautiously and switched on the light of the torch. Almost within arm's length, and partly buried in the slime, was the object which the spy had thrown away.
As the detective hooked at it with his stick a hoarse voice shouted:
"Ahoy there! What are you doing with that light?"
Apparently from nowhere a boat ploughed through the mud until its bows were within a couple of feet of the steps. The next instant Ferret and his companions were covered by a revolver.
It was a naval guard-boat, the watchful eye of the officer in charge having discovered what he took to be surreptitious signalling. Explanations followed, and were accepted. Ferret, holding the recovered prize, ascended the steps, followed by Ross and Vernon, while the boat backed noiselessly away. It was but one more example of the ceaseless vigilance of the great, silent Navy.
Almost dead-beat, Trefusis and his chum made their way to the hotel, had supper, and went straight to bed. Ferret, they decided, could wait until morning.