The diamond pin by Carolyn Wells

A nice mystery novel, although very slow. It dates 1919, and starts with a funny tone, describing rich old Ursula Pell's character, which was a rather peculiar one. She had a thing for nasty pranks, she enjoyed so much her jokes she could not resist the temptation and everybody around her, from the servants to her lawyer, were victims, although nobody suffered from it as much as her niece.
Her nephew Winston Bannard had lived with her for a few years before he could not stand it anymore and decided to live on his own, so now her niece Iris Clyde was her favourite victim.
Iris was at her limit, and would have left home like Winston did, if a tragic circumstance had not prevented it. One night, Aunt Ursula was found dead, assaulted in her room, locked from the inside, with no other possible way in or out. Ursula's great fortune was mostly in jewels, and Iris had been promised a diamond pin in her will, and when she saw that it was in fact "a dime and a pin" she thought of another trick and threw it away. It looked like a very common pin, but soon a man asked her for it, then a masked man entered her room to demand it, then she was abducted in order to get it... she couldn't imagine why, but it was all too much for her, so Miss Lucille Darrell, Ursula's cousin who inherited the house, called for a private detective to solve the mystery: she had no faith in the local police since they arrested Winston for the murder and even suspected Iris for a moment.
Of course Iris and Winston are in love, but one could say: why they never tried to meet each other?
Famous detective Fleming Stone comes with his assistant, a boy whose name is Terence Maguire, but people call him Fibsy, a nice and smart kid, humble and good. This is not a book filled with clues to follow, not at all, just a story to read.
It turns out in the end that Winston had gone to his aunt in the morning, then after he went away Charlie Young, the man that tried in every way to get the pin from Iris, had gone to Ursula to get from her the pin and the receipt, the two important clues to where the treasure is hidden. He tied her up, but left her alive. Despite being shocked and bruised, Ursula said nothing at lunch (which they call dinner, who knows why), then she went to her room alone, locked the door, then had an accident and fell backwards bringing table and lamp down with her, and died. The mystery of the room-locked-from-the-inside this time is unraveled like this: both Stone and Fibs thought of it, because if it was really impossible for anyone to get out, therefore nobody did! :-)
The pin's importance was in the letters engraved in it, a crittograph that needed a word in the receipt to be solved; another little help from Fibs and they find the treasure to be buried between her parents' graves.
The criminal part of the story is a bit ridiculous, actually very much so, always so polite... but nice to read, and all in all this book was a pleasant enough read.