[1] It is the first novel starring fictional reporter Joseph Rouletabille and concerns a complex, and seemingly impossible, crime in which the criminal appears to disappear from a locked room.

[citation needed] Reporter and amateur sleuth Joseph Rouletabille is sent to investigate a criminal case at the Château du Glandier and takes along his friend the lawyer Sainclair, who narrates.

Rouletabille meets and interrogates several characters: the castle's concierges Mr & Mrs Bernier, the old servant Jacques, an unfriendly inn landlord and a womanising gamekeeper, and begins a friendly rivalry with France's top police detective Frédéric Larsan, who has been assigned the case.

Larsan suspects Ms Stangerson's fiancé, another scientist called Robert Darzac, to Rouletabille's dismay.

Two-and-a-half months later, as Darzac's trial opens, Rouletabille reappears sensationally and tells the court that the culprit is Frédéric Larsan himself, whom he accuses of being an alter-ego of a master criminal called Ballmeyer.

During the night, traumatised by the event, she fell off her bed and inflicted the gravest of the wounds by hitting her temple on the corner of her bed-side table.

Ballmeyer, in a different guise, had seduced Ms Stangerson in her youth and married her secretly in the United States.

Ms Stangerson had arranged for her son's care and education and hidden the whole saga from her father; her silence and Robert Darzac's behaviour were motivated by her desperation to keep him from finding out.