Owen Egerton is shaping up to become a new Darren Lynn Bousman. A horror director who sticks (largely) with core genre films, doesn't set out to innovate much when he tackles a horror niche, but executes his films with care and heart for the genre. If you can appreciate that, then Mercy Black is a very fine horror flick.
After spending 15 years in a mental institution, Marina Hess is declared cured and gets to go home. She spent her time there after having assaulted a classmate when she was still a little kid. In Marina's mind, Mercy Black, an urban legend with the power to bring people back to life, was the one who orchestrated the assault. Soon after she's released, she starts to see traces of Mercy Black around her.
If the story sounds familiar, that's probably because there's plenty of films just like this one. But the performances are solid, the build-up of tension is meticulous, the styling is moody and the pacing is just right. This is pure and unfiltered genre work, nothing original, but lovingly crafted and executed. Good stuff.