Situations Vacant by Mick Herron

Everyone has a book in them, it’s commonly said. What’s less remarked upon is how many people have a book waiting for them to step into. Novels don’t cast themselves, after all; for every figure glimpsed halfway through a paragraph – a woman in a pink tracksuit walking a dog; a man muttering to himself while searching his pockets at a bus stop – there’s a real-life prototype somewhere; probably not wearing a tracksuit at all, and nowhere near a bus stop, but nevertheless responsible for triggering a quirk of recognition in the writer, who makes a mental note before passing on by.

And this is handy, because I’m currently on the final draft of the latest Slough House novel, and am mentally auditioning characters for the next book, a standalone. (One of the great things about writing a series of novels featuring the same characters is that, every so often, you can tell them all to buzz off and go play with some new friends instead.) The main characters are spoken for, but there’s any number of background figures I’ll need to call upon – folk to fill the otherwise empty streets – and it’s gratifying to have so many hopefuls to choose from.

Mind you, some people try too hard. The young man on the Tube I saw pencilling marginalia into the Book of Revelations was way too creepy to be an extra. He’ll just have to catch the eye of a horror writer instead. But the young woman who I watched, in the course of a three-minute journey, having her heart broken by a callow youth who preferred to flourish his book-club edition of Crime and Punishment than engage her in conversation: there’s almost certainly a role for her. The brave smile she fixed to her face while fumbling with her iPod’s earbuds has stayed with me ever since.

As for her heartless swain, I’ll bear him in mind next time I need a non-speaking character to walk into a lamp post.

Real Tigers by Mick Herron is out now.