In what appears to be a normal Sunday, the marital relationship between Emma and Alberto is cracked by a single, unsettling question.

Sunday is the day when Emma and Alberto, a quiet and reserved middle-aged couple, spend more time together. Things change when Emma sees their neighbor - a widower - in the company of a woman at the window: has he already replaced his wife? The thought of what Emma herself would do, if her husband was suddenly gone, begins to haunt her and the question slowly makes its way through the folds and frustrations of life as a couple.

Domenica was born from a question: would you replace me if I weren't there anymore? The question arises from a doubt: is it only the circumstance of things that makes us stay together? In a couple, especially in a long-term one, a spark may be enough to destroy the apparent certainties. It is, in fact, during a Sunday that seems like all the others, that a small change - the neighbor grappling with a new "flame" - breaks the habit and empties it of meaning, revealing a bleak truth.