French mass literature has invariably enjoyed great success among Russian readers; Meanwhile, the experience it has accumulated until recently has not been the subject of reflection on the part of domestic scientists. The most productive periods in the development of this sphere of French literature include the end of the 19th – beginning of the 20th century (“the belle époque”), when mass reading, while maintaining its adherence to its traditional narrative and stylistic principles, at the same time underwent significant renewal. This process is especially vividly captured in the work of Gaston Leroux (Gaston Leroux, 1868–1927). In Russia there is not a single study about Leroux, whose works are also not fully represented in Russian translations. The prepared book, in a form accessible to the general reader, examines Leroux’s novelistic work, taking into account his extensive heritage as a journalist. Particular attention is paid to the general context of French mass reading of the “Belle Epoque”. Separate chapters are devoted to Leroux’s stay in Russia and the Russian theme in his prose and journalism; the role of Leroux’s works in the development of detective literature (in comparison with Maurice Leblanc); the poetics of the terrible in Leroux's novels; the architectonics of his large-scale novel cycles (in comparison with the cycle of novels by P. Souvestre and M. Allen about Fantômas).