For some moments Allerton was undecided what to do. At first, under the impression that the mysterious vessel had opened fire, he altered helm in order to prevent the boat masking the destroyer's reply. Even as he did so, he noticed that the tramp was much lower in the water.
"The blighters have scuttled her, by Jove!" he exclaimed. "Lay on your oars, lads. We don't want to be carried down with her."
Without the faintest doubt, the would-be prize was sinking fast. That was undeniable evidence of her guilt. No law-abiding merchant vessel would voluntarily destroy herself simply because she was about to be boarded by a party from a British man-of-war.
With great rapidity the Memnon sank. She did not heel or even roll. She disappeared amid a smother of foam, throwing out a swell that tossed the Windrush's boat like a cork. An oval patch of silvery light from the destroyer's searchlight marked the spot where the mysterious vessel had plunged to the bed of St. Ives Bay.
"Give way, lads!" ordered Allerton. "We may find some of them in the ditch."
For a quarter of an hour the boat hovered around the spot. There were no signs of survivors—not even of débris. A little oil, floating in iridescent patches, alone marked the place, and even that was drifting sullenly with the weak tidal current.
At dead slow ahead the Windrush closed her boat. A mark-buoy and sinker were dropped overboard, the searchlight was switched off and the boat hoisted up and swung inboard.
"Good enough," declared the lieutenant-commander as his sub gained the bridge and reported. "We haven't made a capture, worse luck; but we've done the next best thing. We've scuppered this pirate-johnny, whoever he may be. Right-o, Sub, carry on, please, while I write out my report."
The Windrush had that morning left Devonport under orders to patrol the coast between Hartland and Pendeen Points. Another destroyer was assigned a beat between Hartland and Worms Head, while a third cruised between Swansea Bay and Milford Haven. All outward and homeward bound shipping were to be spoken, and, in the event of any suspicion, to be boarded and have the papers examined.
This was in execution of a general Admiralty order embracing the whole of the West and South Coast of England and the South Coast of Ireland, but it was hardly expected that the mysterious pirate would be found in the approach to the Bristol Channel.