The difference was remarkable. Seth Hooper’s journey to London had been long, bruising and hazardous. Seated on top of a swaying stagecoach, he was exposed to rain, wind, the jostling of other passengers and the multiple shortcomings of roads that were no more than mud-caked tracks. On his return to Nottingham, by contrast, he was one of four passengers travelling inside a mail coach that was cleaner, more restful and much faster. Apart from the driver, there was also a guard outside, dressed in the Post Office livery of maroon and gold, and armed with two pistols and a blunderbuss. Hooper couldn’t believe that he deserved such comparative luxury. He was an interloper. Comfort made him feel uncomfortable.

Peter Skillen, however, was completely at ease.

‘This was a wise choice,’ he said. ‘It’s over a hundred miles to Nottingham. This coach should get us there in less than sixteen hours.’

‘The stagecoach that brought me to London took a lot longer than that.’

‘The person to thank for this mode of transport is John Palmer.’

‘Why is that?’ asked Hooper.

‘He helped to design a vehicle like this. Palmer used to be involved with a theatre in Bath and was always complaining how long it took to move actors and scenery to and fro. To speed up journeys, Palmer hired post-chaises. When he suggested to the government that the Post Office should make use of smaller, lighter, swifter coaches, he was asked for a demonstration of a vehicle very much like this. It was a great success. As a result,’ said Peter, ‘it set the standard.’

‘I’ve never had such a fast ride, Mr Skillen.’

‘Sit back and enjoy it.’

‘I’m in no mood to enjoy anything,’ said Hooper, solemnly.

‘That’s understandable.’

Almost immediately, one wheel of the coach went into a deep pothole and the passengers were thrown violently sideways. It was a timely reminder that, in return for more speed, they would have to get used to such sudden lurches on a treacherous road surface. Their journey, Peter mused, was a metaphor for the task they’d set themselves. In the course of their investigation, there would be an endless series of bumps, wobbles, jarring jolts and uncontrollable swaying. Yet he remained confident that – like the mail coach – they would eventually reach their destination.