Where: A midsized apartment in the center of St. Petersburg.
What: The gas stoves in this apartment are lit using matches; these models do not have an electric spark which ignites when the valve is opened. If someone opens the valve and forgets to ignite the flame or if the flame is blown out by a draft, then the result is the situation described in the note.
Tatyana informed the person who wrote the note of her plans (to spend the night away from the apartment). As an explanation for Tatyana's absent-mindedness the person who wrote the note advances the hypothesis that she was drunk. All of these and other details find their way into the note, written for the purpose of alerting the addressee to the need to check the valve on the gas stove before she goes out.
Since the apartment has few residents (six or seven people) with varying schedules and they rarely encounter each other in the kitchen, the practice of leaving notes and signs makes sense. It is not quite clear why this note, with so many details, and with this content, is addressed specifically to one person, rather than taking the form of a sign written in large letters and posted on the kitchen wall or in the entryway about the need to check the gas valves on the stove before going out.
Compare with other missives from this same apartment: "Concert announcement" and an appeal not to hang underwear in the bathroom.