Many films that deal with the advent of some sort of apocalypse usually hit the ground running, but When Evil Lurks also keeps its sense of panic and paranoia right up to its bitter end. Even during moments of downtime—as this small group of "survivors" tries to keep moving—there is an overwhelming sense that they're only delaying their inevitable suffering, or that evil has existed long before  any of them. There are passing mentions of this demonic presence having originated in the city, and how it manages to infiltrate the lives of those on the outskirts through modern things like electricity and gunfire. It's an intriguing angle that gives possession a new texture: these demons aren't just randomly manifesting, but invading and occupying.

And when the violence kicks in, When Evil Lurks really doesn't spare its characters, as shown by some pretty gnarly practical effects and vicious sound design. The constant escalation of the demonic threat can feel contrived at times—as the rules of how things operate in this world keep on being added or modified, at a rate that can be hard to process—but the anguish it leaves its characters in is suffocating all the same. There may not appear to be a moral at the end of all this, but it evokes a sense of hopelessness better than many other films.

There are a number of disturbing scenes all throughout the movie, but its best moments are still those in its opening half-hour. This is when the film's mystery is still at its most impenetrable, and it's when the danger feels so much more intense. We've come to expect at least some breathing room from horror movies before things start going south, but When Evil Lurks barely gives us time to collect ourselves. The confidence that the film places in its audience—to just go along with the craziness wherever it leads—is admirable stuff, not to mention an example of lean, mean, efficient storytelling.