The life of Sofia Kazimirovna Ostrovskaya (1902–1983) included a lot: childhood in a wealthy family, study at the history department of Petrograd University, service as the head of the criminal investigation department of the Murmansk railway, being under arrest, working as a translator of technical texts, the ambitions of an unrecognized writer, friendships with Anna Akhmatova and others. All this was reflected on the pages of her diary, published in its entirety for the first time, which she kept from a young age until the middle of the 20th century, but the siege of Leningrad occupies a special place in it, described expressively and in detail. Outside the scope of the diary, only Ostrovskaya’s activities as an agent of the special services, in particular in monitoring Akhmatova, remained.