Thorne panicked. Sub smiled. “You forget, Irene. I’m a student of pressure.”

In the grey, drizzling chill of a London February, a different kind of detective was on the case. Not Holmes of Baker Street, but Sherlock Sub — the city’s only underwater consulting detective.

“Look there, Thorne,” Sub murmured, tapping the sonar. A ghost bloomed on the screen: a wreck, not on any chart.

Sherlock Sub lit his pipe—waterproof, naturally—and puffed a ring of smoke that dissolved into the fog.

“Impossible,” Thorne whispered. “They weigh forty tons each.”

They descended. The black water pressed in. Through the viewport, the wreck resolved—not a ship, but a drowned warehouse, its brick teeth grinning in the silt. And inside, stacked like silver ingots: the missing barges.

Sub held up the velvet glove. “The sealant on this glove is the same as the gaskets on the pump. And the manufacturer?” He paused. “They only sell to one person. Irene always leaves a signature. A single, elegant flaw.”

The answer surfaced in the form of a woman’s laugh, echoing through the sub’s hydrophone.

“Elementary,” Sub replied, adjusting his waterproof deerstalker. “The thief isn’t a man. It’s a current. Or rather, a manufactured one.”

“Now, Thorne, the game is still afloat.”

But who?

On the surface, as the river police hauled up diamonds and a furious Irene, Thorne asked, “How did you know the frequency?”

He flipped a switch. A high-frequency pulse screamed from the sub’s speakers—not a weapon, but the precise frequency of the hydraulic pump’s resonance. The drowned warehouse began to tremble. Bricks rained. The pump overloaded, reversing current.