Ten years have elapsed since the events chronicled in The Tragedy of X and The Tragedy of Y. Drury Lane has gotten much older, and is frail and sickly these days. As for Inspector Thumm, he has retired and opened a detective agency, which is doing rather well. More surprisingly than that, we discover that Inspector Thumm has a daughter, Patience, who is the narrator of our story.
It all begins innocuously enough. Elihu Clay, an honest businessman (keep your smart-aleck comments to yourself), comes to ex-Inspector Thumm’s door for help. It seems his business is doing very well… indeed, almost too well. He has a silent partner, Dr. Ira Fawcett, brother of Senator Joe Fawcett, and he suspects the doctor is using his business to pull some financial hanky-panky on behalf of the Fawcett clan. Inspector Thumm accepts the case, but with little hope of success – although it’s widely known that Senator Fawcett is crooked, no one has been able to prove so in a court of law.
Thumm’s daughter Patience comes along for the ride, because even though she has no role in the investigation she’s a Liberated Woman. She hits it off with Drury Lane, making a couple of clever deductions about how the detective is spending his spare time. So when murder comes a-knocking and Senator Fawcett is bumped off, with the police eagerly seizing on the most obvious suspect, Patience consults the Great Detective and brings him onboard to solve The Tragedy of Z.