Peril at Cranbury Hall — John Rhode

A shady operator is targeted for death and needs help from a professor with an “uncanny ability to ferret out the truth” (The New York Times).
 
An expert in alternative medicine is creating a clinic in Cranbury Hall that promises to cure fatigue, and Arnold Gilroy is happy to invest in this promising moneymaking venture.
 
Unfortunately, his brother Oliver has just finished a stint in prison for fraud -- and has weaseled his way into running Cranbury Hall while pursuing some nefarious business on the side. Before long, he's been grazed by a bullet -- and Dr. Lancelot Priestley will have to step in before the killer strikes again, with more success this time, in this Golden Age British mystery.