Some names are easy. Opal Jones in As She Left It had her name when she popped into my head. The working title for the story was Opal Jones Comes Home; it's a terrible name for a mystery but it's fun to say and I said it about ten times a day while I was working on the first draft. And she looks like an Opal.
Late on in the final draft, I realised that I couldn't have a character, in the same book as Opal, who was called Olive. That leads me to one of the few pieces of writing advice I will stand by, no matter what: when changing a character's name from Olive to Norah via global search and replace, watch out for scenes with pizza.
It's not always as easy as Opal Jones. The heroine of the book I'm working on now was born as Tash Harkness and, no matter how I wooed her, she wouldn't come out and show herself. Then I changed her name to Gloria Morrison and boom! She was fifteen years older, with a different job, a completely different personality and a new story she wouldn't shut up about. I feel a bit sorry for Tash Harkness, though, floating around in limbo. Maybe she'll parachute into a new story one day.
I suppose the most important names to get right are those you're going to be living with, year in and year out, in a series, til you're ancient and bitter and dead (it's going well; thanks for asking). And I'm okay with Dandy Gilver. It's unusual enough to be memorable but it's plain enough not be annoying when I type it for the thousandth time.
You've got feel for Agatha Christie, who got so sick of Hercule Poirot that she ended up parodying herself in the character of Ariadne Oliver, who invented a Finnish detective called Sven Hjerson. Some of the irritation was about nationality - Oliver knew as little about Finland as Christie knew about Belgium - but "Hercule" and "Poirot" can't have helped, right?
Some of my favourite names are just flat-out stolen. In the first draft of A Bothersome Number of Corpses I named a gaggle of characters after my brand-new California friends. I always meant to change the names once I had time to research them, but with only a tweak or two these 21st-century American women made perfect 1920s Scottish schoolgirls. Sally Madden was fine, Katie Howard was fine, Eileen Rendahl became the slightly less Scandinavian Eileen Rendall, Stella Ruiz became the quite a lot less Latina (and very posh) Stella Rowe-Issing. Spring Warren worried if maybe "Spring" wasn't a name then. I reassured her that it's not a name now.
And in the newest Dandy Gilver, The Reek of Red Herrings, I've pinched another one. A friend, going through family papers while settling an estate, found an ancestor called Euphemia Clatchie and immediately emailed me. I challenge anyone to think "Euphemia Clatchie" and not get a clear picture of her. Sometimes characters just write themselves . . .