Edgar Wallace 
The Clue of the New Pin [EPUB ebook] 

In this 1923 mystery by Edgar Wallace, Jesse Trasmere is thrifty and does not trust banks, so he keeps all of his money in his prison-like house. Although his nephew, Rex Lander, receives a generous allowance from his uncle, it is not enough for his extravagant lifestyle. Trasmere breaks with routine and informs his valet, Walters, that he is going out of town for a while to avoid an acquaintance from his past. One day he turns up dead, in a completely locked vault, the only clue is a pin found at the scene of the crime… A newspaper reporter helps clear the prime suspect and reveal the identity of the true killer.