The case takes place in early September 1909 on board the Sibir river steamer going upstream. Over the course of one day, a long cold night and an endless foggy morning, an “unexpected accident” will occur here, a series of crimes and a brilliant investigation of these crimes by Prince Alexei Alekseevich Lepekhin, the former director of the police department of the Ministry of Internal Affairs of the Russian Empire, and now a state criminal, following under in a convoy to the place of departure for exile in the city of M. The prince is accompanied on the way by his wife Ekaterina Dmitrievna and his brother Prince Sergei Dmitrievich Rusov.