"That Affair Next Door" by Anna Katharine Green was as delightful as it was gripping - a good old-fashioned mystery in good old-fashioned language.
For a book originally published in 1897, it is surprisingly modern in that the heroine is not only an elderly single woman (and a clever one at that), but one who is happy about it.
Miss Amelia Butterworth is well off and respected in New York's society. Her ideas about life and the people around her are a mix of the conservative and the quirky, resulting in some rather entertaining comments about her neighbours and others she meets in the course of the story.
The house next door to hers has been standing empty for some time, the rich owners being away on a steamer trip to Europe.
One night, though, Miss Butterworth happens to observe a couple arriving at a late hour. They enter the dark and empty house, and after a little while, the man leaves alone.
Miss B. is worried about the lady's welfare - not only must it be very uncomfortable for a woman all alone in a dark and empty house, with no fires lit, no cook to request a meal from, and no maid to make up a bed for her.
But her worries increase when the next day, the house looks and sounds as empty as before, with no sign of the lady who must still be inside. Not even a shutter has been opened on one of the windows.
The police do not take her concerns serious at first, but eventually, entry is gained - and a dead woman found in one of the parlors.
Miss Butterworth's eyes and ears are as sharp as her mind, and she soon draws some conclusions. Detective Gryce, reputedly one of the best The Force has to offer, at first resents her "meddling". But soon the two elderly people develop a mutual respect and realize they need each other's knowledge and wit to solve the mystery.
What lies at the base of the murder, how many people were really in the house that fateful night, and whose hand directed the weapon dealing the fatal blow - it is all revealed in the end, with the tension remaining until the last chapter. A few times I was sure that my guess was the right one (along with Miss Butterworth's), but I was surprised time and time again.
Anna Katharine Green wrote two more books involving Amelia Butterworth (and a total of nearly 40 novels), and I am definitely going to look for some of them. She lived from 1846 to 1935 and has been, according to wikipedia, called "the mother of the detective novel".
She married a man 7 years her junior; they had 3 children.
I found this as a free ebook at Amazon's kindle shop. This was the second time I have read something by A. K. Green; the first time was in 2014, "Initials Only". You can find my review of it here, if you are interested.