Patricia Wentworth 
Death at the Deep End [EPUB ebook] 

A lonely young nanny boards a bus and disappears—and the “marvelous” Miss Silver must investigate (Daily Mail). Anna Ball has disappeared. For a year she has moved from one job as a nanny to another, unable to settle or make friends. After just a month with her last family, she walks down the road, steps onto a bus, and is never seen again. No one notices she has gone. Almost no one. There is one woman who cares about Anna: a long-ago school pal named Thomasina, with whom she would trade a weekly letter. When the letters stop, she panics, knowing that if she doesn’t help the girl, no one will. She seeks out Maud Silver, the kindly spinster detective, and asks for her help. A lonely girl has disappeared without a trace, and Miss Silver smells a whiff of murder in the air.