Ngaio Marsh, originally 1966, 1981 revised edition.
Marsh’s autobiography is unrevealing. Indeed she says as much herself, talking about having involuntarily “withdrawn from writing about experiences which have most closely concerned and disturbed me … I have been defeated by my own reticence”. I like the odd vignette that reflects something in the novels. Here’s the genesis of Death at the Dolphin (1967):
At about this time  another and, to me, most beguiling project was considered by Dan O’Connor. At Woolwich there was a theatre that had received bomb damage and not been repaired. The idea was that, if it could be made usable, a Shakespeare season should be held there during the Festival of Britain. Audiences would be able to “take water to the play” going downstream by barge from Westminster Pier. One sparkling spring morning Tyrone Guthrie (he was not yet knighted), his wife, Bob and I, all went down the river to inspect this theatre. It was the gayest of jaunts. Tony Guthrie was in the middle of producing The Barber of Seville in a lovely licquorice-all-sort kind of setting and he and Judy sang bits of it all the way. We picked up the keys of the theatre at a pub and let ourselves in. The damage was extensive. “No good, dear,” said Tony Guthrie after one glance at it. “What a pity! Never mind.”
This unemphatic hardly-a-description should be set against the pages-long loving description of the Dolphin in the novel, evidently in better nick than the real theatre but still in a bad way, smelling of rats and rot.
He had forgotten about the bomb damage. A long shaft of sunlight from a gap in the roof of the stage-house took him by surprise. It produced the effect of a wartime blitz drawing in charcoal and, like a spotlight, found its mark on the empty stage. There, in a pool of mild sunlight, stood a broken chair still waiting, Peregrine thought, for one of Mr. Ruby’s very own actors. Behind the chair lay a black patch that looked as if a paint pot had been upset on the stage. It took Peregrine a moment or two to realize that this must be the hole the clerk had talked about. It was difficult to see it distinctly through the shaft of light.
Marsh mentions making drawings around the text when she is writing, and Margaret Lewis’s 1991 Ngaio Marsh: A Life shows one of these – group of her characters with added cat. Marsh’s cats kept her company whilst she wrote. I forget whether the characters are the Lampreys or from one of the theatrical books.