Death at Swaythling Court — J.J. Connington

Hubbard made his money in blackmail, most detestable blackmail at that. A wealthy, lisping butterfly collector, there were no special regrets when he was found dead at his desk in his own home. Yet Colonel Sanderstead felt it his duty to probe the affair, since his nephew's best friends had very good reason to wish Hubbard dead.

His investigation, as it turns out, would never have solved the case, but it leads to an amazing confession ...