A frozen island. A monastery turned political prison. A cipher inked in blood. When anarchist poet Katya Efremova is transferred to the prison colony on Solovetsky Island, she finds an enigma among her returned possessions - a blood-stained book containing a cipher left by her murdered mother, written on the day she died. Following her mother's clues, Katya begins to unravel a centuries-old mystery woven into the history of Solovetsky Island.