1913. Former police inspector Alexander Grossmeister, by sheer chance, becomes an agent of Russian counterintelligence under the striking name Labruyère. His assignment is to pose as the owner of a respectable photographic establishment—which, in reality, is a counterintelligence base. War is not far off, and new fortifications are being built near Riga on Magnusholm. The Austro-Hungarian intelligence agency "Evidenzburo" has sent its people to obtain the plans of the fortification area. Intrigues are being woven; the achievements of technical progress are being used; deadly seductresses are putting their charms to work… Labruyère is inexperienced, dissatisfied with his superiors and comrades, and ends up in strange situations—but it is precisely him who manages to uncover the spy network and win the most valuable prize… "The Batteries of Magnusholm" is a direct continuation of the novel "An Airplane for the Winner".