The night was warm and there were occasional flashes of summer lightning. To Harry’s thinking, this made the strange quest they were engaged on all the more uncanny.
At last they reached the cliff.
“I wish another flash would come,” said Ralph, “we daren’t light matches. But I brought along an electric torch.”
“A good idea. We may need it later,” said the inspector. “Hullo! Look there! I guess that explains the mystery of the motor boat’s vanishing.”
Another flash had revealed a tunnel-like hole in the cliff which could hardly be observed from the water side, on account of several thick bushes which grew, either by accident or design, about its mouth.
“There’s a path,” said Ralph presently, as another flicker of lightning revealed a rough trail leading up the cliff face.
“We’ll follow it. Easy, now, boys, we don’t want to give the alarm,” warned the chief inspector.
Through the darkness the intruders on the gem smugglers’ realm crept up the slippery track. At last they gained the top. Below them, as the flickering flashes showed, was a big pool of water, either natural or artificial. Doubtless the tunnel through the cliff led into it, for moored to one side of the pool could be seen the mysterious motor boat.
There were no lights on board her. Apparently those who had arrived at the island had made their way up the hill to the windmill tower, for a light could now be seen gleaming, like an angry eye, half-way up the structure.
“They’re all up there. Collecting their effects preparatory to leaving the island forever, I imagine,” whispered the inspector. “Let’s have a look at their boat.”