Gaston Leroux, of Phantom of the Opera fame, wrote many other books including a series about a detective called Rouletabille, the first installment of which is The Mystery of the Yellow Room, in which a young woman scientist is savagely attacked in the yellow room of the title, a room that’s locked and at the door of which her father sat. Rouletabille, a young journalist, sets out to uncover the truth and finds that many actors in the French castle where the attack took place had secrets, some related to the crime and most not, and has to travel all the way to America to untangle the complicated motives and the shadowy author of the attack.
The book is over a century old, and moves at a very leisurely pace compared to modern mysteries — and most of the action takes place through deduction rather than direct investigation. It also appears that the next book in the series (which I will read soon!) is so heavily foreshadowed in this one that we already know its outcome. Still, a very enjoyable historical tromp.