Why Didn't They Ask Evans? (1934) - A book by Agatha Christie, a murder mystery about the murder of an unknown man

This is another book by Agatha Christie which does not have either of her main 2 detectives, Hercule Poirot or Miss Marple. This book was also published in the United States under a different name - The Boomerang Clue. The book got a good review from the press upon its release.
The book is about a man found murdered near a cliff at the seaside resort town of Marchbolt, who dies shortly after being found by the hero of the book, but before dying, he utters the words "Why didn’t they ask Evans?". He also has a photo in his pocket, that of a young beautiful girl. The book is about the quest of the person who found the dead man, Bobby Jones (the son of the vicar) to explore the mystery of the dead man. In this quest, he runs into danger himself, with an attempt made on his own life through poison. He has a friend, "Frankie" – Lady Frances Derwent, who helps in the quest to first identify the man who died, then find out the overall mystery about why the man died, and who was the person who killed the dead man. As always, Christie does not put too much of romance in these books, but by the end of the book, the lead pair realize that they are indeed in love with each other and get engaged.



Bobby is playing golf with a friend, and when the ball goes over the cliff, he finds a man on the ground who is unconscious, and clearly in a bad way. The man dies, but just before dying, he utters a few words to Bobby. Bobby also has an immediate alternate assignment, and to stay with the dead body, another man known as Roger Bassington-ffrench steps in. Soon, the photo in the dead man's pocket comes forward, identifies herself as Amelia Cayman, and identifies the man as Alex Pritchard.
Bobby gets a job offer from Buenos Aires, but declines. Soon after, he is struck by poisoning when drinking beer, but the police don't find any clues. Soon after, he sees the photograph again which was used for the identification, but realizes that the photo he saw and that in the paper was different (so Roger must have changed the photo). This ensures that Bobby now wants to investigate further, and the best way (as decided and Bobby and Frankie) was to find Roger Bassington-ffrench. Do they manage to find Roger, who was the murdered man, and why was he killed ? Is there any movie involved ? Read the book to find out.