She had long since learned tricks of invisibility. Be still where you can, be as silent as you can, let other small sounds drown your steps. If you cannot fool the eye, then fool the brain—stand where you are not expected and you will not be seen. Keep to the highs, keep to the lows, and avoid eye level if the terrain lets you. But these were tricks for the freckled woodland. Here in the street it was a matter of understanding patterns of flurry and flow. Stillness made one obvious, like a stone in a stream.

Time and again she would knock her bonnet against a swinging milk pail, or nearly blunder beneath the wheels of a cart. Just to keep the teacher in view she was forced to squeeze alongside walls and between bodies, leaving a trail of trodden toes and murmured annoyance.

Thankfully, her quarry seemed cheerfully unaware of the world around him, but this too presented problems. At one point he stopped dead and dropped to a crouch to examine a snail whose shell had cracked beneath his boot. While an oyster seller’s tray tipped dizzily above his head, he could be seen placing together the fractured pieces of the snail’s shell and nudging it gently on its way. By the time he walked away with an oblivious smile, the road behind him was a tangle of tumbled bodies and overturned barrows. Despite herself, Mosca was impressed. The only other creature she had seen cause so much chaos in a ten-second period was Saracen.

She followed the teacher through Riversliver Race, where mackerel shimmered in slick silver heaps, where prawns with gummed black eyes questingly stirred their jointed legs. Through the Hides, where headless turkeys hung over doorways, plucked of all but wispy feather collars and garters, where rabbits dangled like furred gloves. Through a street sickly with the smell of tanners, through a network of alleys and entries. Down to the riverside, and in through the door of a coffeehouse.

“Welcome back, Mr. Pertellis,” said a coffeemaiden at the door as she took the teacher’s hat and coat.

As the door closed behind him, Mosca watched, agape and aghast.

It was not so strange to see the teacher entering a coffeehouse. What Mosca did not expect was for the coffeehouse to judder, grind gently sideways, then abandon the roadside altogether and drift out into the open river.

A violent wind roared in through the newly opened gap, leaving Mosca to wrestle with her ever-rebellious bonnet. The walls of the coffeehouse had been painted cunningly to give the appearance of brickwork, but she saw now that they were wooden. Above the roof swung two broad, square sails. In the sky, at the end of long, strong tethers, tugged six or so diamond-frame kites, most of them only two feet across, but the largest was six feet wide and decorated with a twist of laurel on a white background.