This film is certainly gritty.
Essentially a married couple working at Heathrow airport are on the lookout for new members of their family. They find young adults no one will really miss and kidnap them. Then they start torturing and brainwashing them - making them want to be part of the family by threatening violence for any slight misdemeanor.
It is violent. Very violent at times, and more unsettling because it is all carried out my a middle-aged couple - not a demon in sight - and in the confines of a typical house making it very intimate and intense.
It's a film you may not have heard of. I hadn't particularly - beyond the occasional mention in some of the horror mags. But if you like a bit of gore it might be your thing.