A faint, rapid throbbing was borne to their ears. The sound came not from the sea but along the shore to their left, where a projecting tongue of land limited their range of vision.
"Motor," announced O'Hara laconically.
"And not a marine one," added Denbigh. "Come on. We'll follow this path; it's a jolly sight safer than keeping to the shore."
Once again they plunged into the mangrove forest, following a beaten track that, judging by its well-worn condition, had been in existence long before the arrival of the Pelikan.
Suddenly Denbigh halted and held up his hand. Footsteps were approaching, not those of the naked feet of natives but the booted tramp of white men.
The subs took cover and waited, fervently hoping that the oncomers had not a dog with them. The party advanced slowly and haltingly, so much so that for the moment Denbigh imagined that their suspicions had been aroused.
But without once glancing in the direction of the hidden officers the men passed by. One was a petty officer of the Pelikan. Denbigh recognized him by his bushy beard. With him were four seamen, walking two abreast. The leading pair carried a roll of something wrapped in a painted canvas cover; the others bore a large reel of wire, paying out the thin cable as they went.
"H'm, telephone wire," muttered Denbigh. "That doesn't look as if the ship has cleared out. More than likely they've landed some of the guns to form a masked battery. It strikes me pretty forcibly that we'll have to investigate at both ends of the wire."
Not until the sound of the receding footsteps had died away—and it took an exasperating time—did the subs emerge from their place of concealment. The air was now almost free from mist. Occasionally patches of vapour drifted across their path, but generally speaking the miasmic belt ended at a distance of about half a mile from the sea.
O'Hara stooped and lifted up the wire.