Professor Stangerson's daughter Mathilde is attacked and almost killed in her room, which was locked and bolted from the inside at the time of the attempted murder. Footprints lead out of one of the windows in the pavilion, but the shutters were closed and all the other windows of the building are barred. How did the attacker enter and leave the hermetically sealed room without being noticed by the professor and his servant? It's up to journalist and amateur detective Joseph Rouletabille to solve this classic in detective fiction.
This is an overdue classic where I once stumbled upon the solution and lost the urge to read afterwards, but recently I realized I actually forgot what I read back then and figured I should grab that opportunity immediately. And I'm really glad that I did as this aged surprisingly well considering this was written in 1907.
It does have its flaws though. The impossibility of the locked room is followed by two more seemingly impossible events including one actual murder, but they are rather unimpressive in their solution and improbable in their execution. You could somehow justify them as additional info for solving the novel's central problem of the Yellow Room, but even then there are clues apart from those events that are much more useful and obvious in comparison which also lead to the identity of the culprit and the way in which the problem of the locked room ensued.
And said problem is actually really intriguing in both construction and solution. The initial buildup including the depiction of the mystery itself and the investigation of the locked room's circumstances was the most entertaining part for me together with the solution, which was surprisingly satisfying in spite of the relatively high expectations that were raised in the beginning of the novel. The clues aren't exactly logically leading to only one possible meaning, but they are not so arbitrary that you could say the correct deductions are intangible once you take everything into consideration accordingly. The way the locked room ensues is not inevitable and logical throughout all its factors and layers, but it's simply applaudable considering this was written before and influenced all the locked room mysteries that were to follow. The novel itself also mentions how unique its locked room mystery is in the way that it not only makes it impossible for any human being to enter or leave the room (as in the case of Poe's The Murders in the Rue Morgue), but actually renders the crime scene hermetically sealed for the first time in the history of detective fiction. Furthermore, this was the first locked room that included the element of time in its construction and solution instead of just searching for a way for the murderer to get into the room.
Another flaw might be that the setting with a young journalist like Rouletabille as the detective does not exactly feel authentic, but Gaston Leroux was a journalist himself and even if Rouletabille himself can be rather unimaginable for readers nowadays, the novel depicts the commotion and sensation around such a bizarre and seemingly impossible crime conveyed via the media in a convincing and diversified style.
Other than that, I definitely recommend this classic and not only because of its significance. While there are works where the fun is kind of ruined by its successors, this is still pretty enjoyable and it certainly endured the flow of time.
PS: Sacrificing 7 years of learning French at school to exchange the brain space with knowledge of the Japanese language is regrettable... probably... but the anonymous English translation from 1908 works perfectly fine. If the novel's plot wasn't set in France, I could have thought the original was written in English.