I simply like the idea of pitching and tossing into foreign countries together with your hotel room, without having to endlessly pack and unpack suitcases. I also love the sea (I’ve been told by an astrologist that this is typical for an October Libra baby) but on a beach holiday I’m generally too lazy to move from the sun lounger, enter the water, dry myself off, then reapply the sun cream (as you never know if sun cream really is waterproof just because it says so on the bottle) and all that stress for three mere swimming strokes, because swimming isn’t my thing… whatever, I’m digressing. What I wanted to say was that for people like me who simply enjoy looking at the ocean, long days at sea are ideal.

Passenger 23 is a novel. This should mean that I’ve been lying to you. None of it happened. But, as I’ve said elsewhere, every good lie has a kernel of truth. And in this respect, Passenger 23 has more kernels than a watermelon. For example, the basic principle that a couple of dozen people vanish without trace from cruise ships every year is as true as the claim in the book by Captain Daniel Bonhoeffer that, in the US, large law firms have now specialised in representing the relatives of cruise victims. In fact, I’m sorry to say that all the mysterious missing-person cases Bonhoeffer outlines in chapter twelve are real. I’ve just changed the names of those concerned and of the ships.

In 2011 and 2012 a new sombre record was set: fifty-five people disappeared. If I’d based the novel on these two years alone, I’d have had to call it Passenger 27.5.

I hit upon the idea for this book back in 2008, when I read in Park Avenue (a magazine that has since vanished into the ocean of the periodical market) an article about the phenomenon of passengers that go missing from cruise ships.

The reason it took me until March 2013 to finally get going on the first draft is plain and simple: the flash of inspiration didn’t come until much later – that’s to say the idea that rather than putting a missing person at the heart of my story, I should feature a passenger who resurfaces and whose reappearance alone disproves the suicide theory that cruise lines often advance as a knee-jerk reaction. For it’s also true that the booming cruise industry has no interest in including in those glossy brochures the warning that every passenger with a half-decent brain can figure out for themselves: when several thousand people come together in a small space, conflict is bound to occur. And of the millions of people who now opt for this sort of holiday, you can be sure that not every single one of them is nice.