Social anxiety is bad enough on its own; it's even worse when the seemingly irrational paranoia and fear it spawns is justified. In Citadel, Tommy (Aneurin Barnard) is struck by crippling agoraphobia after he witnesses his pregnant wife, Joanne (Amy Shiels), get attacked by a group of hooded teenagers in their derelict apartment building. Left to care for their prematurely delivered daughter, Elsa, after Joanne dies from the hypodermic-needle-to-the-belly assault, Tommy finds himself paralyzed to function in even the most basic ways.
Using handheld camerawork that clings to a constantly trembling Tommy like a wet blanket, writer-director Ciaran Foy considers his protagonist with empathy, taking time to detail his struggles to make it out the door or to survive therapy sessions in which he's told that his comportment and expressions clearly mark him as a past—and future—victim. Those difficulties aren't soothed by the affections of a kindly nurse, Marie (Wunmi Mosaku), but they're exacerbated after a run-in with a crazed priest (James Cosmo) who, with a brusqueness that borders on but never tips into absurdity, explains to Tommy that the fiends who killed Joanne will soon be coming for Elsa, because, apparently, they're something akin to unholy "demons."
After Marie is also savagely beaten by hooded kids, Tommy turns to the priest. Along with Danny (Jake Wilson), a blind boy who was rescued from the villains' clutches and whose lack of fear is a shield of sorts against them, the priest takes Tommy back to the apartment building to rescue Elsa and torch the place, and send its malevolent inhabitants back to Hell. Whether the film is a pure metaphor for Tommy's recovery from wounded wimp to confident hero is left open-ended by Foy, who drenches the action in symbolic moments that suggest such a reading, right up to a finale in which Tommy travels out of darkness and into light, but never presses the point in a manner that would interfere with the material's suspense.
Citadel is stripped down and no-nonsense, fixating on Tommy's emotional and psychological struggles with an intensity that's harrowing. And if Foy implies, through his depiction of his villains, that delinquent youth are in fact the evil spawn of Satan, any social commentary remains secondary to basic cat-and-mouse, fight-or-flight horror procedures. A few too many formulaic thrills may render the action a little less original than initially hoped for, but in Barnard's tense, terrified countenance, it ably locates fear as a consuming, internal plague from which escape, if possible, is arduous and painful.