I gave tongue, which is the only way a dog has of saying found it, and Mr. Holmes was on his feet again before the sound had properly finished.
The trail took us down toward the river, through streets that grew narrower and smelled increasingly of fish and tar and the mixed stink of a great many people living close together without quite enough water to wash in. This matters to what happened next, which very nearly finished the whole chase for good.
There is a trick that clever men sometimes play on a dog, and I did not know, on this occasion, that anyone had thought to play it on me. Mr. Holmes worked it out afterward and explained it to Mr. Sherman with something that sounded almost like admiration for the man who had tried it. Near the fish market, where a hundred barrows had been standing all day soaking every stone of the street in brine and scale, someone had laid a second trail, deliberate and heavy, of the very same French scent I was following, running off in an entirely different direction toward the bridge.
I nearly took it. For those first few strides it smelled exactly like the trail I had been running for the better part of an hour, and a dog does not stop to ask himself whether a smell has been placed there on purpose, since smell does not arrive with an explanation attached the way a man's words do. I ran perhaps forty yards down that false trail before something in it began to trouble me. It took me a distance to understand what. The true trail had been laid by a moving man, walking, sometimes running, and it thinned and thickened the way a moving man's scent does, stronger where he paused, fainter where he hurried. This second trail did not thin or thicken at all. It sat on the stones with the same even strength the whole way I followed it. That is not how a man smells when he is walking anywhere. It is how a scent smells when it has been poured, all at once, from a bottle.
I stopped again, for the second time that night, and this stopping felt different from the first. Less like failure. More like the particular satisfaction of catching someone in a trick, which I did not know until that night that a dog could feel at all.
I turned back. Dr. Watson, following with the lantern, said something about the dog having lost his nerve. I heard Mr. Holmes correct him, quietly, in a voice that had something like respect in it that I have not often heard a man use about a dog.
"He hasn't lost the trail, Watson. He's found out it was a lie."
The true trail ran not toward the bridge at all but along the river itself, past the fish market and down toward a row of warehouses where the smell of tar was thick enough to make even a human notice it, and where the brine and rot of the water nearly drowned everything else in the world. It was hard going, and slow, and by the last stretch my legs had begun to ache in the way they do now every single day, though that night it was the ache of real work and not the ache of age, and a dog knows the difference even if he cannot explain it.
We came at last to a warehouse with a door standing very slightly open, and here the sweetish scent was so strong and so recent that I did not need to cast about at all. I sat, which is the sign I had been taught for here, right here, no further. Mr. Holmes put his hand briefly on my head, which from him was as good as a whole meal.
What happened inside I did not see, since I was left at the door with Mr. Sherman while the two men went in, but I heard a good deal of it, a dog's ears being nearly as useful as his nose when the walls are thin, which these were. A man's voice, young, frightened in a way that had none of the young woman's lavender fear in it, more the fear of a man caught rather than a woman worried. Mr. Holmes's voice, level and unhurried, laying out the whole shape of what had happened before the man had a chance to deny any of it.
I gathered enough afterward, from what Dr. Watson told Mr. Sherman over a glass of something in the back room, to piece the story together. He said Mr. Holmes had gone into that warehouse and laid the whole thing out before the young man had managed a single word of denial, telling him the French scent, the forced latch, the two years since his engagement had been broken off, and the debts he had brought home from France along with his climbing skill, in that same level voice he used for reading out a train timetable. The young man had tried, weakly, to claim he had only come to the warehouse to meet a friend about some shipping business, and Mr. Holmes had asked him, not unkindly, which friend, and what business, and whether he would object to Dr. Watson fetching a constable so the friend could confirm it, and the young man had said nothing at all after that, which Dr. Watson took, correctly, as an answer in itself.
The young man had been engaged to Miss Ellery some two years before, and had been cast off by her family for want of money, and had gone abroad, to France, where he had come by both the scent that clung to his stolen boots and a certain skill at climbing he had never had honest cause to use. He had returned to London that autumn, poorer than when he left, and had convinced himself, in the way a desperate man convinces himself of almost anything, that a necklace he had once seen Miss Ellery wearing, a family piece worth a good deal more than sentiment alone could account for, would set him up somewhere new if only he could get it away clean.