They caught him on the third night of watching, and it was Diccon, of all people, who spotted him first.
The boy had begged his way onto the tower rotation on the strength of his sharp eyes and his stubborn insistence that a future Disciple of the valley ought to be trusted with more than vellum and ink, and Thomas had relented, against Victoria's initial objection, on the condition that he was never posted alone. It was Diccon's low, urgent whistle — the signal Elias had taught the whole watch that week, deliberately different from anything used before, in case the stranger had learned their old patterns — that brought Wat's men converging on the eastern slope before the figure moving through the gorse had covered another fifty yards.
He didn't run, which surprised Thomas more than anything else about the encounter. He simply stopped, hands raised, and waited with a stillness that suggested he had already calculated the odds of escape and found them wanting.
He was younger than Thomas expected, dark-haired, dressed in plain traveling wool that gave away nothing until Wat, searching him with rough efficiency, produced a small leather case from beneath his cloak — papers, carefully sealed, and a compact brass instrument Thomas recognized after a moment as a crude but genuine surveying level.
"Not a soldier," Elias said, examining the level with open professional interest despite the circumstances. "A man who measures things for a living. That's a good instrument. Better than mine, if I'm honest."
The stranger said nothing at first, watching them with the wary, assessing calm of a man deciding how much of the truth would actually help him. It was Victoria, arriving breathless from the gatehouse with a lantern, who finally got him talking — not through threat, but by switching, on a hunch, from the March's rough country speech into the more careful, formal Latin she'd learned as a girl for exactly this kind of encounter.
His name, he admitted eventually, was Corradino, and he had been sent — he was careful, even under pressure, not to say by whom — to observe and report on "matters of trade innovation" in the northern March, on behalf of interests he described only as "a house with correspondents in several cities."
"Genoa," Wat said flatly, not a question.
"Perhaps. Perhaps somewhere else. I am paid to look, not to explain who pays me to look." Corradino's accent was faint but unmistakable, his composure returning now that the immediate danger of violence had passed. "You will not get a name from me tonight, whatever you threaten. I have been in worse rooms than this one."
"The fire," Thomas said. "The dye shed. Was that you?"
For the first time, something like genuine offense crossed the man's face. "I observe. I do not burn. Burning draws exactly the kind of attention my employers pay me to avoid." He looked, briefly, almost insulted by the accusation. "If your dye shed burned, Lord Thomas, you have a different enemy than the one standing in front of you. I would have thought that obvious, given how carelessly whoever did it left evidence for your mapmaker to find. I have been considerably more careful than that for the better part of a year."
Victoria's expression, in the lantern light, went very still. "A year."
"A year," he confirmed, with something that might have been professional pride under different circumstances. "Since word first reached certain trading houses that a valley in this March had developed a currency that held its value without debasement, and a medicine that reduced fever deaths among children by a margin no physician in Genoa or Florence could match. Such rumors are common. They are almost always false. I was sent to determine, quietly, whether this one was different." He inclined his head slightly, an oddly courtly gesture from a man with his hands still bound. "I will tell my employers, when I am eventually permitted to leave, that it is."
"And if I don't permit you to leave at all?"
"Then another will come in my place within the year, better prepared for the reception I received tonight, and you will have gained nothing but my employer's confirmed suspicion that you have something worth protecting badly enough to disappear a man over it." Corradino said it without malice, the way Hamo once discussed a column of figures — simply stating a fact he expected the room to be capable of absorbing. "I would advise, if my advice carries any weight in your decision, that you release me with whatever message you'd like carried back to Genoa, and spend your genuine concern on whoever burned your dye shed instead. I promise you, Lord Thomas, that is not a courtesy I would extend to a rival."
Thomas looked at Victoria, and found her already arriving at the same uneasy conclusion he was — that the stranger's honesty, however self-serving, rang truer than any denial would have.
"Elias," he said finally. "Escort him to the ridge road at first light. Unharmed. And Corradino — tell your employers exactly what you've seen here, currency and medicine both. I'd rather have Genoa's honest interest in trading with us than Genoa's dishonest interest in stealing from us."
Corradino's eyebrows rose, fractionally, the closest thing to surprise Thomas had seen from him all night. "That is not the answer I expected."
"It's the only one that doesn't cost us more than it saves." Thomas held his gaze. "But you'll forgive me if I don't entirely believe you weren't involved in the fire, whatever you claim. I intend to keep watching regardless."
"I would expect nothing less," Corradino said, and, for the first time, something that might almost have been respect crossed his composed foreign face. "It is, if I may say so, the only reason my employers find you interesting enough to watch at all."