The Emerald Catherine the Great by Hilaire Belloc

Marjorie had insisted upon seeing her father alone, and she had worked it easily enough.

The Professor in his relief from the accursed emerald had fallen into a sprightly mood. He had compelled young Galton to take a _second_ walk, and therein had bored the turfist to agonies; which only shows that God is just, and that we are punished in that by which we sinned; in Galton's case, the avenue. During that walk the crystallographist volubly explained his exciting experiences in the past as an amateur detective. His large prattling mouth discoursed of marvellous sleuth-deeds in the past. But he did not go too far. He said nothing of emeralds. He kept the tit-bit, the great revelation, for his host -- and he knew at what time to deliver it.