Mara Ironfoot's three nights of shadow-watching produced a window on the fourth day, and she sent word to Brekk before first light.

Tonight. Two hours past midnight. The blind spot holds for approximately eleven minutes.

Brekk had been preparing for this since her first report, and the preparation had two parts that needed to happen at the same time in different places.

The first part was four people, Mara and Torr and two others, moving toward the depot's downslope approach using the route Mara had surveyed two seasons ago, before any of this had a reason to exist.

The second part was Brekk himself, with the remainder of the Ravine's warriors, conducting a harassment sortie against the Ravine sector's main Threian position at the same hour.

Loud enough and persistent enough that anything the depot might send toward the Ravine in response would be looking south, not toward its own downslope edge.

The sortie began first. Brekk's people hit the Threian position's eastern perimeter with the harassment pattern they had used for weeks, withdrawal before contact could become decisive.

Except this time the withdrawal was slower, the engagement allowed to run longer than the pattern usually permitted. Tonight the point was not to inflict damage efficiently.

The point was to be seen, for as long as possible, by as many people at the Ravine position as could be made to look.

Mara's team moved while the Ravine position's attention was occupied.

The downslope approach was steep enough that the Threians had judged it not worth guarding, and Mara's route knowledge confirmed why. A near-vertical section partway up required handholds that were not visible from above.

She had found them two seasons ago, and nothing about the terrain's appearance from the depot's side would suggest they existed. They climbed it in silence, Torr second in the line, the other two warriors carrying the tools.

The winch frame sat at the shelf's eastern edge exactly as Mara had drawn it.

The blind spot Mara had been tracking was the shadow the frame itself cast across the sentry position's typical sightline. It rotated with the moon, and for eleven minutes tonight, it covered the approach to the frame's base completely.

The axle sat in a wooden sleeve at the frame's pivot point, greased, turning freely under no load.

Mara had described exactly what needed to happen to it. One of the two warriors who carried tools did it: a fine abrasive compound, worked into the sleeve's interior surface.

The axle's rotation would grind it slowly with every use, invisible once the axle was reseated, indistinguishable from ordinary wear until the sleeve's surface degraded enough to bind.

It took four minutes. They were back over the vertical section with two minutes of the blind spot remaining.

The sortie at the Ravine position wound down an hour later, Brekk's people withdrawing in the controlled, unhurried way that suggested nothing unusual had happened.

As far as the Ravine position's defenders were concerned, nothing unusual had. A harassment sortie that ran a little longer than most, on a night like any other.

Mara's team reached the Ravine position before dawn. Brekk met them at the eastern watch point, the same place he had read every report that had come to him since this had started.

"Four to six uses," Mara said, without being asked. "The abrasive works into the sleeve with every rotation under load."

"Their cycle is six per day. At four to six uses, the sleeve degrades enough to bind under the counterweight's full load, and the axle seizes."

"How long is that, in days."

"One day, possibly less, before it seizes."

"After that, they will try to free it, re-grease it, reseat it, the things you try when something that has always worked suddenly does not. None of that will work, because the problem is the sleeve's surface, not the grease or the seating."

She paused. "A forward depot does not carry a spare winch sleeve. They will need to fabricate one or have one brought up from further south."

"How long for that."

"I do not know their supply situation well enough to say precisely. Days, at minimum."

"While they wait, the water comes up by hand, in smaller loads, more trips, more people on that slope at predictable times, because hand-hauling does not have the flexibility a winch has."

Brekk looked north, toward the depot, invisible from here but present in the way that things you have spent weeks thinking about are present even when you cannot see them.

"This is not a victory," he said.

It was not a question, and Torr, beside him, did not treat it as one.

"No," Mara said. "It is a condition that did not exist yesterday and exists now."

"What it becomes depends on what we do with it, and we do not yet know exactly when it becomes anything, because we do not know exactly when the sleeve binds."

"So we watch."

"So we watch, and when the hand-hauling starts, we will know within a day, because a depot that size hauling water by hand changes how it looks from a ridge."

"More people, different hours, different formation on the slope." She sat down on the cold stone, the same stone Brekk had sat on three days ago when she first laid out the depot's drawing. "I will write this for Kael the same way I wrote the first assessment. What we did, what we expect, and what we do not yet know."

Brekk nodded and watched the dawn come up over ground that had not changed at all, that morning, in any way a person standing on it could have seen.

Somewhere north of them, a counterweight winch sat in its frame exactly as it had the day before, turning freely, carrying water up a slope it had carried water up every day for longer than the Ravine position had existed.

It would keep doing so for perhaps one more day, or two, before something inside it that no one watching would notice simply stopped working the way it always had.

That was the work. Not the moment on the slope in the dark, though that had mattered.

The work was the day after, and the day after that, when something that had always functioned quietly stopped functioning, and the people who had caused it to stop were the only ones who knew why, and could be ready for what came next because of it.

Brekk went down to check the warrior positions, the same as every morning, and began the day's accounting.