In "One of These Days" by Gabriel García Márquez, a poor, unlicensed dentist by the name of Aurelio Escovar is called upon by the local mayor to extract a painful infected tooth. At first, he's reluctant to perform such an operation. But once the mayor threatens to shoot him, he has no choice but to comply.
The threat of violence indicates just what kind of a man we're dealing with here: the mayor is a bully who thinks nothing of intimidating people to get what he wants. Not only that, but he's hopelessly corrupt. He steals from the public treasury with total impunity. We see this when Escovar asks him where he should send the bill, to the mayor or to the town. "It's the same damn thing," comes the reply.
But before Escovar concludes his dental work, he stands up to the mayor, realizing that, on this unique occasion, he is now in a position of power. With his patient lying vulnerable on the dentist's chair beneath him, Escovar has the confidence to tell the mayor, "Now you'll pay for our twenty dead men," meaning that the pain he's about to endure will be payback for the deaths of twenty men for which the mayor is in some way responsible. Either through corruption or violence, or maybe even a combination of both, the mayor is a killer, and he's about to get his comeuppance.