Edgar Wallace 
The Clue of the New Pin 

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.