The coastline was irregular, convoluted. Sano and Hirata navigated around partially submerged rock formations and jutting spits of land. Above them, the woods loomed like a windswept, rustling black wall. Waves lapped the shore. Ears alert for any guiding sound, Sano strained his eyes against the darkness.

Nothing.

Then, reaching the point where they’d seen the lights vanish, they came upon a narrow cut in the coastline.

“The lights must have gone in there.” Hirata propelled the boat into the channel. There the darkness was almost complete, with only the faintest moonlight penetrating the overhanging foliage. The boat scraped against the sheer rock walls that lined the channel. The splash of the oars echoed. Not knowing what to expect, Sano gripped his sword, preparing for a clash with ghosts or men, while his heart drummed a quickening rhythm of anticipation.

Now the channel curved sharply left and opened into a circular cove. Moonlight illuminated a steep, rock-strewn shore with woods above and the mouth of a cave in the center. From within the cave’s recesses, a purple light shone.

Hirata guided the boat to the right of the cave. Sano stepped out and helped his retainer lift the vessel ashore. With Hirata close behind, he tiptoed to the cave’s opening, sword drawn, and peered inside.

Stone walls and an arched ceiling, purple in the light’s eerie, smoky glow, enclosed a short passage. The sea filled its bottom; narrow ledges ran just above the waterline. At the rear of the passage, the floor slanted upward to form a landing. There sat a boat; the light shone from some sort of fixture on a pole in its bow. Otherwise the cave was empty. The boatman had vanished.

They cautiously sheathed their swords. Motioning Hirata to follow, Sano entered the cave. He crept sideways along the ledge, clinging to the rough surface of the wall. They stepped onto the landing and over to the boat.

The vessel, perhaps fifteen paces long, was heaped with wooden crates. Sano examined the light fixture, a pyramidal metal lantern of strange design, with a door on each face. One door stood open; inside, a metal cup attached to the support pole held a substance that burned a brilliant, blinding purple and emitted black smoke. Sano turned a crank on the side of the lantern and, by a clever system of gears, belts, and levers, the other doors opened and closed in sequence. Through them he saw two more metal cups, which held residues of what he surmised had once burned green and white.

“The mysterious lights,” he said, his voice echoing in the cave. A man-made device—fashioned by Abbot Liu Yun, or by the Dutch?

Hirata pried the lid off a crate inside the boat. “Look at this!”