She emailed the Society from Monaco. Sensible, successful, not remotely the type to imagine things — and absolutely certain that someone was following her. Only ever when she rode her moped through the city alone. Same helmet in the mirrors, always two corners back, never closer, never gone. The local police had checked precisely once, seen nothing, and suggested she vary her route. Holmes read her email twice and booked us flights that evening. It’s the only when she’s alone that got him. Patterns like that don’t imagine themselves.

The plan was simple. She’d ride her usual route; I’d wait at the quiet end of it, where the road drops down towards the marina; Holmes would be somewhere unspecified, being Holmes. Sure enough, along she came — and behind her, two corners back, the helmet. I did what any reasonable man who’s been to too many self-defence classes would do. I knocked him off his moped and we went at it on the marina decking, which I can now report is considerably harder than it looks.

Mid-fight, a few things became clear. He was blocking rather than swinging. He kept shouting “I’m not the one following her!” And he was, I had to admit, making a fair point, because she was already half a mile gone and he’d shown no interest in anything but my right hand. He wasn’t the stalker. He’d noticed the stalker — weeks ago, apparently, and had been shadowing her ever since to make sure nothing came of it. There’s a longer story about who he is to her, and it’s theirs to tell, not mine.

The actual stalker, meanwhile, had done what Holmes expected: used the commotion to get ahead of her, where the road narrows by the harbour and a car can box a moped in nicely. What he didn’t know was that Holmes had spent the morning rearranging the harbour road — one borrowed hi-vis vest, two stolen traffic cones, and a diversion sign pointing somewhere the road doesn’t go. The stalker took the diversion at speed. The diversion, as designed, was the boat ramp. His car went into the harbour at a pace I can only describe as satisfying, and Monaco’s harbour does not accept apologies.

He was fished out, arrested, and turned out to be exactly the kind of man you’d guess: someone from her past who believed money and menace were the same thing as a claim on her. Case closed. She still rides the same route, no helmets in the mirrors. I still check the decking for my knuckle marks. And Holmes kept the hi-vis vest, which worries me for future cases.