The genesis of "Clown" started in 2010 with a fake trailer and a really cool idea. The 77-second video, purported to be for a horror film directed by Eli Roth but really the work of aspiring filmmaker Jon Watts, took the web by storm and caught the attention of Roth himself. Agreeing to produce, the "Hostel"/"Cabin Fever" helmer attached his name to the project and gave Watts and co-writer Christopher Ford the opportunity to adapt the trailer into a full-length feature. The results live up to the early hype. "Clown" is imaginatively wicked, but its subjective ghastliness never gets in the way of its subversive sense of fun. Coulrophobics, however, will be less than thrilled.

When the clown hired for son Jack's (Christian Distefano) birthday party abruptly cancels, realtor Kent McCoy (Andy Powers) is determined not to disappoint the little fellow. Rifling through a closet in the house he is currently showing to potential buyers, he comes upon the perfect old costume and promptly slips it on. The party goes off without a hitch, which is more than can be said for Kent's white facial make-up, red nose and rainbow-colored wig. No matter how hard he scrubs and pulls, the clown garb appears to be fastened tightly to his body. Wife Meg (Laura Allen) is initially amused, then frightened as she watches her husband begin to physically and mentally transform. As Kent sets out to track down the origin of the costume and break the curse he is under, he is gradually overcome by an insatiable hunger for children.

"Clown" comes with a humdinger of a premise, and director Jon Watts stylishly milks it for all it's worth. The idea of a person experiencing a physiological metamorphosis into a monstrous clown is very much a variation on vampire lore, right down to the victim-turned-villain's need to feed on humans (or, more specifically in this case, unsuspecting kids). A little suspension of disbelief is required here and there—why, for example, doesn't Kent immediately see a doctor when his one-piece outfit latches onto his body rather than foolishly try to cut it off himself with an electric jigsaw?—but Andy Powers (2005's "In Her Shoes"), as Kent, sells the unthinkable reality of an unrealistic situation. The fear of losing oneself to an uncontrollable disease is bad enough, but multiplied all the more with Kent's realization that his painted-faced visage is just the first step in a full-on cannibalistic transfiguration.

"Clown" can be brutal and ballsy—children of a certain age do not fare well as the story progresses and Kent's changes take over his being—and yet the knowledge that the infected father's precocious son, Jack, could become his next target exponentially raises the stakes. Kent has a family that he loves and cares about, just as desperate wife Meg loves him enough to consider crossing moralistic boundaries of her own to help him. Laura Allen (2009's "Old Dogs") commits to Meg's emotional path and affectingly conveys her torn feelings over trusting Kent while still in disbelief over what is happening to him. Great character actor Peter Stormare (2013's "Hansel & Gretel: Witch Hunters") also shows up for a sturdy supporting role as Karlsson, a man who holds the grave answers to what Kent is going through and how to stop it.

The most difficult hurdle to get past with "Clown" is understanding why Kent keeps his chilling predicament hidden from authority figures and medical professionals. Even if they ultimately couldn't help him, at least it would be a way to prove that he isn't just going crazy or orchestrating an elaborate hoax. As far as everything else, director Jon Watts hits the bull's-eye by developing an empathetic human story to go along with his circus-hued nightmarescape and fascinatingly crafted historical-fiction exploration of the clown as an iconographic figure of cheer and menace. Watts proves unafraid to tackle his plot head-on, even journeying to Chuck E. Cheese for an expertly suspenseful set-piece taking place in the plastic maze-like tubes of a play construction. The mischievous use of Nirvana's little-known track, "Everybody Loves the Clown," over the end credits is a perfect closing touch. From its jokey birth as a faux trailer to its unique development into a fully formed picture, "Clown" has defied the odds. This is an eerie, auspicious, classily mounted fable of the macabre.