Fairly routine story about the death of Gervase Wickenden, a wealthy single man, and the battle for his fortune between his heirs - a motley group of nieces and nephews. His body found alongside train tracks not far from his home, the face crushed beyond all recognition, can only be identified by his clothing and personal effects. An inquest rules the death an accident. Enter Dr. Priestley who smells foul play. He and his secretary, Harold, discover a bullet hole in a fir tree opposite the accident site and are determined to prove that Wickenden was shot and that the "train accident" was done after the murder to obliterate any signs of a bullet wound. It's a bit repetitive in the telling with lots of rehash and recapping as if it were a serial (This is a unfortunate practice of Rhode/Burton in his early books).
For me the best part of the book was the character of Nancy Wickenden -- an outspoken, no-nonsense, modern woman who dares to live with a man and remain unmarried. Her dialog is sparkling and witty. The scene where the uptight and conventional Supt. Haslet visits her apartment and finds a different man and woman (Nancy's brother and his girlfriend using her place in lieu of a hotel) in the apartment is hysterical from a 21st century point of view. Also, Wickenden's lady friend to whom he was engaged is a lively and modern character.
Priestley plays a peripheral role providing the police with the impetus to pursue the case then disappears into the background until the end when he serves as the murderer's confessor in the rather Anthony Wynne-like final chapters. The murderer, suffering from injuries received in a motor vehicle accident and with only hours to live, tells a long-winded tale of the past revealing Wickenden to be a sadistic rogue who allowed his seemingly devoted wife to suffer a cruel death when he tired of her. The crime turns out to be a vendetta years in the making similar to the one constructed by the killer in Queen's Tragedy of X. Even the most astute reader would never be able to figure any of this out and it's far from the kind of "fair play" plot expected from a writer who was a member of the Detection Club.
This was the first Rhode book I read from start to finish. My judgment is that he gets a raw deal as a writer whose books are boring. Tragedy on the Line held my interest all the way despite its unfair ending. I have also read The Claverton Mystery which is a remarkable detective novel on many levels. However, Priestley overall seems too intellectual and lacking humanity in a kind of Holmesian way for him ever to be one of my favorite detectives in the genre. Though I should add once or twice he shows a sense of humor in Tragedy on the Line and, at end of this book at least, exhibits a tender compassion.