Several books titled (The Unlocked Door) are available in FB2 and other digital formats, written by different prominent Russian authors. Depending on your preference for a crime thriller or a sentimental drama, you are likely looking for one of the following: 1. " Незапертая дверь " by Alexandra Marinina
You can purchase or read it on platforms like LitRes or find community-shared versions on Flibusta . 2. " Незапертая дверь " by Maria Metlitskaya
This is a classic detective novel featuring the famous investigator (Book #23 in the series).