At the end of Roald Dahl's "Lamb to the Slaughter," there seems to be no regret from Mary for killing her husband with a frozen leg of lamb and then cooking for and feeding his police coworkers.
The narrator is very matter-of-fact when describing the task of Mary killing her husband, who had just come home and confessed that he wanted a divorce and was involved with someone else (this is implied, but not stated). The wife then goes downstairs, pulls out a frozen leg of lamb and wallops her husband in the back of the head. He collapses and dies immediately.
The narrator makes it a point to make sure the reader understands, "how clear [Mary's] mind became all of a sudden." This sort of eliminates the argument that Mary completed this act out of shock. While the murder can't be classified as premeditated, Mary's actions after the slaughter make it clear that not much remorse is involved.