Thud!

Willikins reported.
    “Thank you.” Vimes stretched, and looked across at Sybil. “Well, this is where we find out. Hang on to Young Sam.”
    “I’m sure Mustrum wouldn’t do anything dangerous, Sam,” said Sybil.
    “I don’t know about that,” said Vimes, opening the door. “I’m sure he wouldn’t mean to.”
    He swung himself out and hauled himself on the roof of the coach, with a helping hand from Detritus.
    The coach was moving well. The sun was shining. On either side of the highway, the cabbage fields lent their gentle perfume to the air.
    Vimes settled down beside the butler.
    “Okay,” he said. “Everyone holding on to something? Good. Let ’em go!”
    Willikins cracked the whip. There was a mild jolt as the horses stretched, and Vimes felt the coach speed up.
    And that seemed to be it. He’d expected something a little more impressive. They were gradually going faster, yes, but that in itself didn’t seem very magical.
    “I reckon about twelve miles an hour now, sir,” said Willikins. “That’s pretty good. They’re running well without—”
    Something was happening to the harnesses. The copper discs were sparking.
    “Look at der cabbages, sir!” Detritus shouted.
    On either side of the road, cabbages were bursting into flames and rocketing out of the ground. And still the horses went faster.
    “It’s about power!” yelled Vimes, above the wind. “We’re running on cabbages! And the—”
    He stopped. The rear two horses were rising gently in the air. As he stared, the lead pair rose, too.
    He risked turning in his seat. The other coach was keeping up with them; he could clearly see Fred Colon’s pink face, staring ahead in rigid terror.
    When Vimes turned back to look ahead, all four horses were off the ground.
    And there was a fifth horse, larger than the other five, and transparent. It was visible only because of the dust and the occasional glint of light off an invisible flank; it was, in fact, what you got if you took away a horse but left the movement of a horse, the speed of a horse, the…spirit of a horse, that part of a horse which came alive in the rushing of the wind. The part of a horse that was, in fact, Horse.
    There was hardly any sound now. Perhaps sound was unable to keep up.
    “Sir?” said Willikins quietly.
    “Yes?” said Vimes, his eyes streaming.
    “It took us less than a minute to go that last mile. I timed us between milestones, sir.”
    “Sixty miles in an hour? Don’t be daft, man! A coach can’t go that fast!”
    “Just as you say, sir.”
    A milestone flashed past. Out of the corner of his ear, Willikins heard Vimes counting under his breath until, before very long, another stone fell away behind them.
    “Wizards, eh?” said Vimes weakly, staring ahead again.
    “Indeed, sir,” said Willikins. “May I suggest that once we are through Quirm, we head straight across the grass country?”
    “The roads up there are pretty bad, you know,” said Vimes.
    “So I believe, sir. However, that will not, in fact, matter,” said the butler, not taking his eyes off the unrolling road ahead.
    “Why not? If we try to go at speed over those rough—”
    “I was referring obliquely, sir, to the fact that we are not precisely touching the ground anymore.”
    Vimes, clinging with care to the rail, looked over the side. The wheels were turning idly. The road, just below them, was a blur. Ahead of them, the spirit of the horse galloped serenely onwards.
    “There’s plenty of coaching inns around Quirm,” he said. “We could, er, stop for lunch?”
    “Late breakfast, sir! Mail coach ahead, sir! Hold tight!”
    A tiny square block on the road ahead was getting bigger quite fast. Willikins twitched on the reins, Vimes had a momentary vision of rearing horses, and the mail coach was a dwindling dot, soon hidden by the smoke of flaming brassicas.
    “Dem milestones is goin’ past real fast now,” Detritus observed in a conversational tone of voice. Behind him, Brick lay flat on the roof of the coach with his eyes shut tight, having never before been in a world where the sky went all the way to the ground; there were brass rails around the top of the coach, and he was leaving fingerprints in them.
    “Could we try braking?” said Vimes. “Look out! Haycart!”
    “That only stops the wheels spinning, sir!” yelled Willikins as the cart went by with a whoom and fell back into the distance.
    “Try pulling on the reins a little!”
    “At this speed,