Demon. Coven, #10.5

Don't let your guard down. When Kathy and friend Trisha are at the club, Trisha's date suddenly collapses, putting an end to their evening. Over the next few days, Kathy notices her friend acting weird. What's worse is that bad luck seems to follow Trisha everywhere she goes. Suspecting something magical might be going on, Kathy begins to investigate to discover just what has gotten into her friend and why exactly Trisha's date collapsed at the nightclub.
And the longer that Trisha is under the spell of whatever demonic magic that holds power over her, the more destruction follows in her wake. Demon is a short story in the Coven series, which serves as a prequel to the Under the Moon series.