Nobody in the tower
A watch tower no longer shoots on its own. It needs its watchman inside, and until she gets there, the Cinderkin have the field to themselves.
A watch tower used to be a machine. Build it, have the haulers bring it bolts, and from then on it shot every Cinderkin that came close, all by itself, every night. Nobody had to stand in it. Put a few round a field and the nights were trivial.
Now a tower has a watchman, one, and it only shoots with her inside. She is on duty from 22:00 to 06:00, climbs the ladder when her watch starts and sleeps through the day, the same hours the watch at a guard post keeps. Inside, she shoots any Cinderkin within 4 tiles, one bolt a second. With nobody in it, a tower full of bolts is just a tall shed.
The film is in Ashwell. A tower stands near the old shaft at the foot of the mountain, ten bolts in its store, with a field of wheat beside it that is nearly ripe. Its watchman is Rosalind Dyer, who lives in a tent at the camp with Henry Dyer. At 22:00 her watch begins, and at the same hour a pack of four comes out of the shaft.
By 22:05 the pack is inside the tower’s reach, and nothing happens. Rosalind is still back by the fire, and the tower is a long walk from there. The Cinderkin wander into the wheat while she crosses the meadow. It takes her until 22:54 to reach the ladder and climb in. From that moment the tower shoots, and by 23:14 three of the four are down.
You cannot see her up there yet. Inside the tower she is hidden, the same as anyone who goes indoors, so for now the bolts are the only sign that someone is on watch.
What I like about it is that a tower now has a place in the town, not just on the map. Built right next to the shaft, it covers the field, but its watchman has a long walk every night before it does anything. A tower is only as quick as the person who has to get to it, and for most of the first hour of that night, Rosalind was still on her way.