In a communal apartment in the fictional Soviet city of Tukhachevsk, lives Katerina Suvorova - a former guide at the local art museum, a member of the so-called Paper Church - an underground Christian circle. Having endured the mills of punitive psychiatry, Katerina fears persecution and writes a secret diary intended for her son. In these notes, the heroine teaches him how to properly wash windows and pray, talks with him about "Robinson Crusoe" and about worshiping saints, and also tells fragments of her own tragic biography. Her notebook is a testament to immense maternal love, which upon closer examination turns out to be a testament of a different kind: about saving the soul through faith and compassion, which has no place in an inhumane system.