Maren's list arrived the following morning.

  Folded inside an unsealed envelope, delivered by a young guard who knocked on Crowe's office door with the expression of someone who had been instructed not to ask questions. Crowe had an office on the third floor of a townhouse in Lower Londrivar — not out of any need for space, the room was small, but for the location: central enough to reach any neighbourhood in reasonable time, anonymous enough that no one remembered the building.

  The office had a desk, two chairs, a bookshelf with less books than space, and a window overlooking a rooftop covered in copper pipes. Crowe used the space for thinking more than for working — there was very little in it that could be called comfortable, which was intentional.

  He opened the envelope standing, by the window.

  The list had seventeen names. Maren had been efficient — each entry had a name, occupation and address, organised by category. Six watchmakers or precision instrument makers. Four academics affiliated with the applied sciences in the Upper Quarters. Five dealers in rare mechanical parts and components. Two with no defined category, listed simply as collectors, private circle.

  Crowe read the list twice.

  On the second reading, three names received a discreet mark on the paper — not because they were more obvious, but because they generated more questions. The first was an instrument maker in the Industrial District with an address Crowe recognised from a different context, without being able to immediately place which one. The second was one of the academics — affiliated with an institution he knew had been closed four years ago for reasons the official records described as administrative restructuring. The third was one of the collectors, with no occupation listed beyond the category, and an address in the Upper Quarters on a street Crowe knew to be expensive enough that anonymity was a choice, not a circumstance.

  He folded the list. Put it in his pocket.

  There was a logic to the order of visits and he applied it without needing to deliberate: start with the most accessible, end with the most closed. The maker in the Industrial District first — industrial environments had a directness that academic and aristocratic ones did not. People who worked with their hands tended to answer direct questions with direct answers, even when they would rather not.

  He buttoned his coat, went downstairs, and stepped out into Londrivar.

  The Industrial District was forty minutes on foot to the east.

  The transition between neighbourhoods in Londrivar was not abrupt — it was gradual, like a shift in mood. The streets narrowed by degrees, the buildings shed their ornament, the smell changed. First damp stone and wood, then oil and metal, then the thick hot steam that was the District's permanent signature — not the light vapour of ordinary streets, but dense, heavy steam, with a weight that settled into the coat and the throat.

  The sounds changed too. The regular click of gears replaced the human noise. Hammers in rhythm. Valves releasing pressure at intervals that seemed almost deliberate.

  The instrument works of Ellard & Company occupied a street with no official name — like several in the District — identified by a number painted on the wall and a metal sign above the entrance that had lost half its letters to rust. What remained read LLARD & CO — INST. OF PRECI—, which was sufficient.

  Crowe went in.

  The interior was tall and open, with an iron ceiling supported by beams that sweated condensation. Workbenches in rows, each with a worker hunched over something small and delicate — the kind of work that seemed impossible in that environment of noise and heat, but which was clearly done there regularly enough that the workers had long since stopped noticing the paradox.

  A man approached before Crowe had taken two steps. Fifty years old, leather apron, a manager's expression — not hostile, but appraising.

  — Can I help you?

  — I'm looking for the person responsible for bespoke instrument manufacturing — said Crowe. — Unconventional pieces. Calibration to the client's own specification.

  The man examined him for a moment.

  — That would be Mr. Vael — he said. — But Mr. Vael is not available today.

  — Since when?

  A small pause. The kind that happens when the true answer is different from the convenient one.

  — Since the day before yesterday — the man said.

  Crowe was quiet for two seconds.

  — Does Mr. Vael live on the premises or does he have a separate residential address?

  — Sir, I can't—

  — I'm not asking for the address — said Crowe, with his usual calm voice. — I'm asking whether he has a habit of disappearing for days without prior notice.

  The manager's expression closed slightly. Not with anger — with discomfort. The difference was important.

  Taken from Royal Road, this narrative should be reported if found on Amazon.

  — No — he said, at last. — That is not his habit.

  Crowe nodded once. He took a card from his pocket — plain, just the name and an address — and handed it over.

  — If he appears — said Crowe — or if anyone appears asking about him — let me know.

  He left before the manager had decided whether he'd agreed or not.

  On the pavement, standing in the hot steam of the District, Crowe took the list from his pocket and looked at the first marked name.

  Vael, R. — instrument maker, special commissions.

  Beside the name, he added a different mark from the others.

  The same kind of mark he had made beside Voss's name in his case notebook, two days ago.

  Disappeared. Without warning. Without explanation.

  There were two of them now.

  He put the list away. He looked at the street ahead — the steam, the gears, the workers moving in and out of windowless buildings. Somewhere in this city, something was finding people who knew too much about the interval.

  And it was doing so with an efficiency that suggested it was not in any hurry.

  That was, in a way, the most unsettling part. Haste implied urgency, implied reaction, implied something that could be anticipated. No haste implied something else.

  It implied pattern.

  Crowe started walking toward the Upper Quarters. The academic with the closed institution was next. And then the collector with no full name and an address too expensive to be coincidence.

  He had the whole afternoon.

  And the feeling — growing slowly since Voss's flat — that the time he had was less than it appeared.

  The institution that had housed Professor Callum Drest occupied a building in the Upper Quarters that was now something else — an engineers' association, according to the new plaque above the entrance. Crowe didn't go to the building. He went to the residential address Maren had listed, two streets behind it, in a townhouse of yellowed brick with a second-floor window whose curtain was slightly open.

  He knocked.

  There was a delay. Then footsteps — quick, light, belonging to someone who had been close to the door without opening it.

  The door opened.

  The man who appeared had sixty years of considered living in his face — not wear, but use, the difference between someone consumed by time and someone who had spent time deliberately. White hair, reading spectacles still on his face, a closed book in his left hand with his thumb inside marking the page. He was dressed in house clothes, which at this hour of the morning was either carelessness or intention.

  His eyes, however, were alert. Very alert for someone who had just opened the door to a stranger.

  — Mr. Drest — said Crowe.

  — Yes — said the man. His voice was calm. Also alert.

  — My name is Crowe. I'm investigating the disappearance of Aldric Voss.

  Something crossed Drest's face. Quickly — a second or less. Crowe catalogued it: not surprise. Recognition.

  — Come in — said Drest.

  Drest's sitting room was the opposite of Ashcroft's office.

  Where the archivist accumulated, the professor organised with an almost aggressive austerity. Few books, all in a straight line. A clean desk with a single open notebook. Two armchairs by the window, one bearing the marks of frequent use and the other clearly decorative.

  Drest sat in the worn armchair. He indicated the other to Crowe, who sat.

  — You knew Voss — said Crowe. Also not a question.

  — We corresponded — said Drest. — For some years. On matters of mutual interest.

  — The interval.

  This time the recognition in Drest's face lasted longer. There was something beyond it — something Crowe identified as relief. The kind of relief of someone who had been waiting for a conversation and had nearly given up expecting it to come.

  — You found the archive documents — said Drest.

  — Two of them. And the list of disappearances.

  Drest nodded slowly. He set the book on the table with care, as though he needed both hands free for what he was about to say.

  — How long have you been investigating this? — said Crowe.

  — Twenty-two years — said Drest. — Since my research assistant disappeared during an experiment I had designed. — A pause. — He was the seventeenth case on the list. I was young enough to believe there was an explanation I simply hadn't found yet.

  — And now?

  — Now I'm old enough to know there is an explanation — said Drest. — It's simply not the kind I had imagined.

  Crowe was quiet. It was the most useful tool he had in moments like this — silence with attention, which worked differently from empty silence.

  Drest looked at the window for a moment. Then at Crowe.

  — The interval is not a metaphor — he said. — It is not a philosophical concept or an instrument failure. It is a real physical state — a condition in which two points in space that should be contiguous present between them a measurable discontinuity. A gap. — He paused. — Voss was trying to map where those gaps exist in Londrivar.

  — And the nameless client — said Crowe. — The one who commissioned the calibration.

  Drest looked at him with attention that shifted slightly in quality.

  — How do you know about a client?

  — Voss's receipt notebook. An entry with no name, three days before the disappearance.

  The professor was silent for a long moment.

  — I don't know who it is — he said, at last. — But I know what they wanted. If someone went to Voss to calibrate an unconventional instrument in this specific context — they were trying to measure the gaps with precision. Not map them. Measure them. There's a difference.

  — What difference?

  — Mapping is observing from the outside — said Drest. — Measuring is entering the system. — He looked at his hands. — Voss was the finest precision instrument maker Londrivar had. If someone wanted an instrument capable of measuring the interval with enough precision to interact with it —

  He didn't finish the sentence. He didn't need to.

  Crowe sat for a moment, the connections forming at the speed they always formed — too fast to narrate, too slow to call instantaneous.

  Voss had calibrated the instrument. Had tested the diagram on the window as a final verification. Had seen the interval. And had vanished.

  Not as a victim.

  As a result.

  — The instrument Voss calibrated — said Crowe. — Where is it now?

  — If it worked — said Drest, with the quiet voice of someone delivering a conclusion they don't like carrying — it went with him.

  The room was silent.

  Outside, Londrivar groaned and smoked, entirely indifferent.

  Crowe stood. Drest did too, by reflex.

  — I'll need everything you have — said Crowe. — Correspondence, notes, anything Voss sent in the last few months.

  — I have it — said Drest. — But Crowe —

  He stopped. Crowe waited.

  — The assistant who disappeared — said Drest. — He was curious. Intelligent. He got close. — A pause. — You are getting closer than he did.

  Crowe looked at him for a second.

  — I know — he said.

  He left with a folder of correspondence under his arm and the headache more present than it had been all day — pulsing behind his left eye with a regularity that, were it mechanical, someone would call precise.

  He had one more name now. Drest. Twenty-two years of investigation, one lost assistant, and enough caution to still be alive.

  And he had a new question, more important than all the ones before it.

  The nameless client had commissioned an instrument to measure the interval with enough precision to interact with it.

  Which meant there was someone in Londrivar who was not trying to understand the interval.

  They were trying to use it.