“Ah,” said Pennyroyal, thoroughly uncomfortable now.

“I’m going to bed,” said Hester. “I’ve got a headache.” It was true; a few hours of Pennyroyal’s lecturing had set a fierce, throbbing pain behind her blind eye. She went to the pilot’s seat, meaning to kiss Tom goodnight, but she didn’t like to with Pennyroyal looking on, so she quickly touched his ear, said, “Call me when you need a break,” and headed aft to the stern cabin.

“Whoops!” said Pennyroyal, when she had gone.

“She’s got a bit of a temper,” admitted Tom, embarrassed by Hester’s outburst. “But she’s lovely really. She’s just shy. Once you get to know her…”

“Of course, of course,” said Pennyroyal. “One can see at a glance that beneath that somewhat unconventional exterior she’s absolutely, um…” But he couldn’t think of anything good to say about the girl, so he let his voice trail away and stood looking through a window at the moonlit mountains, the lights of a small town moving on the plains below.

“She’s wrong about London, you know,” he said at last. “I mean, wrong about it being burned to clinker. I’ve spoken to people who’ve been there. There’s a lot of wreckage left. Whole sections of the Gut lie ruined in the Out-Country west of Batmunkh Gompa. Why, an archaeologist of my acquaintance, a charming young woman by the name of Cruwys Morchard, claims to have actually been inside one of the larger fragments. Sounds extraordinary; charred skeletons scattered everywhere, and great chunks of half-melted buildings and machinery. The lingering radiations from MEDUSA cause coloured lights to bob among the debris like will-o’-the-wisps… or should that be wills-o’-the-wisp?”

It was Tom’s turn to grow uncomfortable. The destruction of his city was still a raw wound inside him. Two-and-a-half years on, the afterglow of that great explosion still lit his dreams. He didn’t want to talk about London’s wreck, and so he steered the conversation back towards Professor Pennyroyal’s favourite subject: Professor Pennyroyal.