“All right,” she said, and snatched the explorer’s purse, counting out five gold sovereigns before he had time to change his mind. Beside her, Tom was saying, “We can make up a bed for you in the forward hold, Professor, and you can use the medical bay as a study if you wish. I was planning to stay here tonight and pull out at dawn.”

“If it’s all the same to you, Tom,” said Pennyroyal, flashing that odd, nervous glance towards the docking ring again, “I’d rather be off straight away. Mustn’t keep my muse waiting…”

Hester shrugged, and up-ended the purse again. “We’ll leave as soon as the harbour master gives us clearance,” she said. “There’ll be a two sovereign surcharge.”

The sun went down, a red ember sinking into the haze of the western Tannhausers. Balloons were still rising from the trading cluster below, airships and dirigibles still coming south across the basalt uplands from great Arkangel. One of them belonged to an amiable old gentleman called Widgery Blinkoe, an Old-Tech antiques dealer who made ends meet by renting out rooms above his shop in Arkangel’s harbour district, and by acting as an informant to anyone who would pay him.

Leaving his wives to moor the ship, Mr Blinkoe hurried straight to the harbour master’s office and demanded, “Have you seen this man?”

The harbour master looked at the photograph which Mr Blinkoe pushed across his desk and said, “Why, that’s Prof Pennyroyal, the historical gentleman.”

“Gentleman my hat!” cried Blinkoe angrily. “He has lodged at my home these past six weeks, and he ran off as soon as Airhaven came in sight, without paying me a penny of what he owes! Where is he? Where can I find him, the creature?”