The plow blade drops while Moody Street is still dark, and the first pass throws a clean white arc against the curb. Munoz Services Corp clears the driveways and walks of Waltham, that old watch-making town folded along the Charles, where brick mill walls hold the low winter light and the streets climb crooked toward Prospect Hill. There is a plain satisfaction in a lot scraped down to bare, dark pavement before the day's first car pulls out, in salt laid ahead of the freeze, in a path opened straight and square to the door. When a storm comes grinding up the river valley and buries the town overnight, the work is simply this: to give Waltham back its footing by morning.