It is interesting and has some of the main ingredients, namely Character, Inciting incident, Action, Goal, which are all really important.

I feel it lacks Stakes, which are implied, but we need more: what will happen if she does not untangle the cause of his death? Is there something original or spicy there? This is extremely important: Stakes.

Also, some specificity would elevate it.

Can we get a characterization for the mistress? What type of person is she? Why are we reading her story? Is she young? Is she poor? Is she a trained boxer? Or an orphan who is left alone in the world? Why is he her lover and not her husband? What will she gain or lose? (Again, stakes)

Another piece is the Problem or the antagonist and the conflict. This is implied, but what will she come up against in her quest for justice? Think ancient Greek tragedies.

Another thing, would be the mention of the World. What type of place and society does she live in? Is it a city? Is it a dystopian future or ancient Rome?

Finally, try to bring some Irony in the mix to truly make it unique.

Hope this helped 🙂