The little slice of sky opened out into huge-huge-endless sky, and howling wind, and suddenly Max was a lot less sure about her plan; but by this time she looked as suspicious as it was possible to look, and Klaus would certainly know what she had been up to. And she really didn’t want to be thrown off a train in the middle of the Bulgarian countryside. So she wriggled her legs through, crouched on the roof of the train, and slammed the hatch shut.

She was just in time. But there was no time for relief: there was only horror.

Wind screamed past her as though it was fleeing something, and it pulled at her skin as if it would tear it from the bones, and battered her lungs when she tried to breathe. The rain flew at her. The noise deafened her. She had to get back inside.

She began to crawl, very slowly, plaits flying behind her like flags.

She only just saw the tunnel in time.

Throwing herself flat on the train, Max barely missed the tunnel roof. The frozen air of the tunnel hit her like a wall of water. For a few long seconds, there was only blackness, and the tortured wind. Then they burst back out again.

She crouched, now alert for anything overhead, and when she felt sure of her balance she began to crawl up to the end of the carriage. The gap between this carriage and the next turned her stomach. But there was no other way forward, and Max had to find the next door. She stretched forward her hands first – then followed them with her right foot, then her left – and crossed the divide.

She carried on crawling. This must be, she thought, what the spider felt like. Scuttling along in a world that was enormous and full of meaningless noise and always likely, with a sudden swoop, to kill you.

Being a spider, she decided, was horrendous.

At last, she reached the next hatch. She had to lie flat for a minute more to avoid some low-hanging wires that crackled and sparked as the train passed. Then she heaved the hatch open, wriggled her body around (oh, horrible, horrible) – and clambered, shaking, back into the train.

She was at the end of a corridor. It was empty. She collapsed with relief on to the floor.

It was stupidly dangerous, said Sister Marguerite’s voice in her head. But since you’ve pulled it off, I’m glad.

For several minutes, Max just lay there in the blissful quiet, curled up tight, shaking. All her resolve began to weaken. She missed Sister Marguerite and her mother and her home and she wanted, more than anything, to just be taken care of for a moment. But nobody was going to do that.