There must be some kind of disease that causes people to talk like that, and the name for it must be something like Airline Syllable Stress Syndrome. It’s the disease that seems to kick in at about ten thousand feet and becomes more and more pronounced, if that’s a good word to use in this context, with altitude until it levels out at a plateau of complete nonsense at about 35,000 feet. It makes otherwise rational people start saying things like “The captain has now turned off the seatbelt sign,” as if there were someone lurking around the cockpit attempting to deny that the captain has done any such thing, that he is indeed the captain and not an impostor, and that there aren’t a whole bunch of second-rate and inferior seatbelt signs that he mightn’t have been fiddling about with.

Another thing that Dirk reflected on as he settled back into his seat was the curious coincidence that not only does the outside of an aircraft look like the outside of a vacuum cleaner, but also that the inside of an aircraft smells like the inside of a vacuum cleaner.

He accepted a glass of champagne from the cabin steward. He supposed that most of the words that airline staff used, or rather most of the sentences into which they were habitually arranged, had been worked so hard that they had died. The strange stresses that cabin stewards continually thumped them with were like electric shocks applied to heart-attack victims in an attempt to revive them.

Well.

What a strange and complicated hour and a half that had been. Dirk was still by no means sure that something somewhere had not gone terribly wrong, and he was tempted, now that the seatbelt sign had been turned off by the captain, to go and take a bit of a casual stroll through the aircraft to have a look for his quarry. But no one was going to be getting on or off the aircraft for a little while now, so he would probably be wiser to restrain himself for an hour. Or even longer. It was, after all, an eleven-hour flight to Los Angeles.

He had not been expecting to go to Chicago today, and the sight of his quarry making a beeline for the check-in desk for the 1330 flight to Chicago had made him lurch. However, a resolution was a resolution, so after a brief pause to make sure that his quarry hadn’t merely gone up to the check-in desk to ask directions to the tie shop, Dirk had made his way light-headedly to the ticket sales desk and slammed plastic.

Overwhelmed with his sudden solvency, he had even booked himself business class. His anonymous employer was obviously someone of means who was not going to quibble over a few minor expenses. Suppose his quarry was travelling business class? Dirk would not be able to keep tabs on him from a seat stuck in the back of the plane. There was almost an argument there for travelling first class, but not, Dirk reluctantly admitted to himself, a sane one.

But, an hour and a half after the plane had taken off, Dirk was beginning to wonder. As a business-class passenger he was denied access to the first-class section up in the nose of the plane, but could wander freely wherever else he liked. He had wandered freely up and down each aisle three times now, surreptitiously watched each of the toilet doors, and seen his quarry nowhere. He returned to his seat and pondered the situation. Either his quarry was in the first-class cabin or he was not on the plane.

First class? He just didn’t look it. The fare would be quite a few months rent on his flat. But who knows? Maybe he had caught the eye of a Hollywood casting director who was whisking him over for a screen test. It wouldn’t be difficult to slip into the first-class cabin and have a quick look around, but it would be difficult to do it without attracting attention.

Not on the plane? Dirk had seen him heading in towards passport control, but there had been a moment when he had suddenly looked round and Dirk had ducked quickly into the bookshop.

A few seconds later, when Dirk next glanced up, his quarry had gone—into, Dirk had assumed, passport control. Dirk had lingered for a decent interval, bought some newspapers and books, and then made his way through passport control and into the departure area himself.

It had not especially surprised him that he had not spotted his quarry anywhere in the departure area: it was a shining maze of pointless shops, cafés, and lounges, and Dirk felt that there was nothing to be gained by rushing around hunting for him. They were being funnelled inexorably in the same direction anway. They’d be on the same plane.

Not on the plane? Dirk sat stock still. Thinking back, he had to admit that the last time he had actually physically seen his quarry was before he had even gone through passport control, and that everything else was based on the assumption that his quarry was going to do what he, Dirk, had decided he was going to do. This, he now realised, was actually quite a large assumption. Cold air trickled down his neck from the nozzle above him.

Yesterday he had inexpertly boarded a bus while tailing this man. Today, it seemed, he had inadvertently boarded a plane to Chicago. He put his hand to his brow and asked himself, honestly, how good a private detective he really was.

He summoned a cabin steward and ordered a glass of whisky, and nursed it as if it were very ill indeed. After a while he reached into his plastic bag of books and newspapers. He might as well just pass the time. He sighed. He drew out of the bag something he had no recollection of putting there.

It was a courier delivery packet, which had already been opened. With a slow frown developing on his forehead, he pulled out its contents. There was a book inside. He turned it over, wonderingly. It was called Advanced Surveillance Techniques. He recognised it. He’d had a flyer for it yesterday in the post. He’d screwed it up and thrown it to the floor. Folded between a couple of pages of the book was the exact same flyer, flattened and smoothed out. With a deep sense of foreboding, Dirk slowly unfolded it. Scrawled across it in felt tip, in handwriting that was oddly familiar, were the words “Bon Voyage!” The cabin steward leaned across him. “Can I freshen your drink, sir?” he said.