I wrote about NIKI Etsuko's first novel 猫は知っていた (The Cat Knew, 1957) last year. 私の大好きな探偵 (Watashi no daisukina tantei, My Favourite Detective, 2009) is an anthology of her short stories. There are five short stories, written between 1958 and 1971. As in 猫は知っていた, the detectives are NIKI Yuutarou and his sister Etsuko (the narrator), except in the last one where only Etsuko appears.Yuutarou is a botany student, tall, thin, calm and rational, Etsuko is a music student, short, plump, lively and inquisitive. In the stories that the two share, Yuutarou contributes most of the deductions.
The first story, みどりの香炉 ('The Green Incense Burner' 1961), is a juvenile detective story, featuring the two detectives as middle school children. Unlike the other stories in this collection, the crime is not murder, but theft. The clues, too, are of the kind one might expect to meet in a detective story for children. The second, 黄色い花 ('Yellow Flowers', 1957) is the murder of a neighbour, found, in the hanare of his house. (Really, just stay out of the hanare. Those places are death traps.) The hanare is locked from the inside, as was the victim's custom; but it's not a locked room mystery, since there are two open windows, through which the murderer could enter and leave. This seems to me a slightly stronger story. The next story, 灰色の手袋 ('The Grey Glove', 1958) is the longest in the collection, the murder and robbery at a cleaning service. Compared to 黄色い花, this seems a more confident piece of storytelling. This time there is less emphasis on deduction, simply an explanation of what was really going on in the story. The readers are left to decide for themselves whether the answer was really discoverable by reason. The other stories, 赤い痕 ('The Red Mark', 1958) and ただ一つの物語 ('Just One Story', 1971), follow the same pattern. In ただ一つの物語 Etsuko is now married, with two small children. The story starts when Etsuko sees a request in the paper from a woman looking for the children's story 'Little Bear Bay'. Bay is Etsuko's son's teddy bear; and the story only exists as a handwritten book. A friend of Etsuko had written it for him, shortly before she died. The move towards a more interesting story, at the cost of exact fair play, is carried even further in this; but I suspect that on rereading one would find that it is quite well clued.
The book as a whole would probably fit into what nowadays are called 'cosy mysteries', particularly the last story, with an emphasis on daily life with small children. Both detectives are amateurs, coincidentally involved in crimes that happen around them. The style is humorous, though not relentlessly so.