He laid his hand on Francis’s arm with a gesture for silence, then, invisible below, someone said, “Fifteen fathoms,” and again the oars creaked audibly in the rowlocks.

Michael took a step towards his cousin, so that he could whisper to him.

“Come back to the boat,” he said.  “I want to row round and see who that is.  Wait a moment, though.”

The oars below made some half-dozen strokes, and then were still again.  Once more there came the sound of something heavy dropped into the water.

“Someone is making soundings in the channel there,” he said.  “Come.”

They went very quietly till they were round the point, then quickened their steps, and Michael spoke.

“That’s the uncharted channel,” he said; “at least, only the Admiralty have the soundings.  The water’s deep enough right across for a ship of moderate draught to come up, but there is a channel up which any man-of-war can pass.  Of course, it may be an Admiralty boat making fresh soundings, but not likely on Boxing Day.”

“What are you going to do?” asked Francis, striding easily along by Michael’s short steps.

“Just see if we can find out who it is.  Aunt Barbara asked me about it.  I’ll tell you afterwards.  Now the tide’s going out we can drop down with it, and we shan’t be heard.  I’ll row just enough to keep her head straight.  Sit in the bow, Francis, and keep a sharp look-out.”

Foot by foot they dropped down the river, and soon came into the thick mist that lay beyond the point.  It was impossible to see more than a yard or two ahead, but the same dense obscurity would prevent any further range of vision from the other boat, and, if it was still at its work, the sound of its oars or of voices, Michael reflected, might guide him to it.  From the lisp of little wavelets lapping on the shore below the woods, he knew he was quite close in to the bank, and close also to the place where the invisible boat had been ten minutes before.  Then, in the bewildering, unlocalised manner in which sound without the corrective guidance of sight comes to the ears, he heard as before the creaking of invisible oars, somewhere quite close at hand.  Next moment the dark prow of a rowing-boat suddenly loomed into sight on their starboard, and he took a rapid stroke with his right-hand scull to bring them up to it.  But at the same moment, while yet the occupants of the other boat were but shadows in the mist, they saw him, and a quick word of command rang out.

“Row—­row hard!” it cried, and with a frenzied churning of oars in the water, the other boat shot by them, making down the estuary.  Next moment it had quite vanished in the mist, leaving behind it knots of swirling water from its oar-blades.

Michael started in vain pursuit; his craft was heavy and clumsy, and from the retreating and faint-growing sound of the other, it was clear that he could get no pace to match, still less to overtake them.  Soon he pantingly desisted.