When Colin hit the Times bestseller list, I’d be the first in line applauding.

Even leaving aside all the cloak-and-dagger stuff, there were practical problems on the horizon. Colin’s life was based three quarters in Sussex and one quarter in London, while I was due to return to Cambridge — the American one — in May.

But it was only February now. May felt a very long time away. I could deal with May when I got there. And in the meantime, I had extended visits with Colin both in London and Sussex, a grilled cheese and tomato sandwich on my plate, and a full cup of coffee in front of me, with free refills to come. Life was good. Life was very, very good.

It only seemed fair to pass some of the happiness along.

I beamed across the table at Colin’s sister, Serena, who was doing a very good job of toying with her salad without actually eating any of it. Next to her, Colin’s friend Martin was devouring his pasta Bolognese as though personally determined to eat enough for both of them.

That wasn’t exactly how I had planned for lunch to go when I decided to take Serena up as my personal project.

It wasn’t that Serena was frumpy or dowdy or any of the usual devices of those teen movies where the more popular girl takes on the plainer one and makes her into prom queen. When it came to sartorial sense, Serena was several steps ahead of me. She had that fragile thinness so beloved of fashion magazines and whoever those cruel people are who create designer jeans: long, elegant bones with only the bare rudiments of skin over them. Her hair was long and soft and shiny and naturally straight and her face had the sorts of interesting hollows one gets from weighing about twenty percent below one’s recommended body weight. She was the sort of girl whose hair never frizzes and whose skirt never gets rumpled.