The receding tide, revealing wet sand, corresponded with Sherlock and John's arrival. Kneeling, heedless of soaking-wet knees, Sherlock's face gleamed hidden knowledge.

"John, look at this. Listen as the sand sings."

"…right. And the tune is.. catchy?"

Sherlock stared, patiently; "Use your eyes, everything's here. Observe!"

"Ears. You said 'singing'."

"Then listen to the ode. The grain of delicacy, revealed by the vast waters. The song of the Thames plucking in perfect harmony with the evidence, lost forever to an untrained eye. See this?"

"It's different soil."

"Obviously. Now, hear the siren's call."

Watching Sherlock work, John had little option.