Demons, angels, werewolves, oh my! Playing much like bad fan fiction from an immature, lovelorn teenage girl who's seen "Twilight," "Beastly," "Star Wars," and "Buffy the Vampire Slayer" too many times, "The Mortal Instrument: City of Bones" is interminable gobbledygook. The latest destined-to-fail ploy for box office dominance adapted from a young-adult fantasy novel (this one by Cassandra Clare), the film spends the bulk of its unruly 130-minute running time buried in convoluted exposition, yet is destined to still alienate anyone who hasn't read the book—the first in a series of six. Murky motives blur with uninspired CGI overload, an undernourished ensemble too big for its britches, and a romance that turns from emotionally arctic to skin-crawling with a single revelatory plot point. This one is a really tough sit.

New York City teen Clary Fray (Lily Collins) has no time to enjoy her approaching birthday when she witnesses a murder at a nightclub, followed by the discovery that her mom, Jocelyn (Lena Headey), has been abducted. She is approached by Jace Wayland (Jamie Campbell Bower), who informs her she, like him, is a shadowhunter—that is, a half-human/half-angel warrior destined to fight the demons invading this world and the alternate one that normal humans, or "mundanes," cannot see. Backed by Jace, best friend Simon (Robert Sheehan), and fellow shadowhunters Alec (Kevin Zegers) and Isabelle (Jemima West), Clary is led to the stately Institute, rumored to be the oldest building in Manhattan, where she learns more about who she is and sets out to find her mother. To do so, she must find the hidden Mortal Cup, one of three holy instruments which the powerful Valentine (Jonathan Rhys Meyers) wants for his own devious purposes.

"The Mortal Instruments: City of Bones" is like every youth-targeted fantasy-romance of the last ten years combined, only with the absurdity of the silly, nearly impenetrable plot magnified. Director Harald Zwart (2010's "The Karate Kid") and first-time screenwriter Jessica Postigo go on for what seem like days trying to explain the story and what is going on, and yet viewers who have not read the book will still walk away no more clear about the reasons Valentine wants this holy cup, why it is important, and what he hopes to achieve. A character pile-up builds throughout, virtually all of them good-looking ciphers and no one but perhaps Clary and Simon worth giving a passing interest in. To care about these two is even stretching it; Clary is a determined girl, but not very appealing as far as protagonists go, while Simon is stuck pining quietly for his lifelong best friend, who is ambivalent to his feelings and ready to hop on the hotter, moodier Jace the first chance she gets. Hop on and smash faces she does, her passionate first kiss with Jace occurring in a greenhouse as the sprinkler system laughably rains down upon them. One scene later, they're sparring over who threw him or herself at whom. What these two dim bulbs do not yet realize may be the one thing that could tear them apart for good. Let's just say late "Flowers in the Attic" author V.C. Andrews would have even recoiled at this turnabout.

In 2012's acerbic fairy tale "Mirror Mirror," Lily Collins made for a lovely and fair Snow White. Playing the slightly harder-edged Clary, the actress flounders with the kind of embarrassing material that would do no favors to even Meryl Streep. "I am not a mundane!" Clary exclaims early on, offended by the suggestion. Collins' forced romantic relationship with Jamie Campbell Bower (2011's "Anonymous"), doing his best impression of a heroin-chic male model as Jace, works neither thematically nor physically, the two of them getting unwanted laughs whenever they're trading flowery sweet-nothings. "Remember when I said I'd never seen an angel..." Jace groan-inducingly tells Clary late in the picture. Ouch. As for Clary's devoted pal Simon, played by Robert Sheehan (2011's "Season of the Witch"), when he finally admits his feelings to her, she acts shocked, then lets him down with a faux-sincere reassurance that just comes off as callous. The one-shot-and-done suggestion that Simon has been bitten by a vampire never comes up again, the character free to wander around and jealously look on when he sees Clary and Jace making eyes at each other.

A movie that combines so many supernatural forces it might sound from afar like a can't-miss proposition—yes, there are also vampires and probably the Creature from the Black Lagoon if you squint hard enough—"The Mortal Instruments: City of Bones" is a messy, derivative trifle. Visual effects range from passable to surprisingly undistinguished—it's a sad state of affairs when 2013 water CGI doesn't even approach the skill of the similar effects work in 1989's "The Abyss"—rarely, if ever, strong enough to seamlessly blend with the live-action surroundings. The film moves at the speed of a starfish race, or maybe it just seems that way because it's so egregiously uninteresting. Nevertheless, there is no sense of discovery or genuine magic herein, while Clary basically takes things as they come without Lily Collins properly conveying what it is she stands to lose if she fails. In all two hours-plus of these dopey goings-on, there is precisely one impressive set-piece involving Clary's possessed downstairs neighbor Dorothy (CCH Pounder). For two or three minutes, the film comes to life, complacency temporarily replaced with palpable danger and a savvily threatening make-up job that transforms consummate character actor Pounder (2009's "Orphan") into a demonic troll crossed with Leatherface. Immediately afterwards, it's back to the dull, corny, third-rate slog at hand. A sequel to "The Mortal Instruments: City of Bones," subtitled "City of Ashes," has already been greenlit and is scheduled to start filming one month after its predecessor's release. For about one hundred different reasons pertaining to this one's quality and chances for success (or lack thereof), studio Screen Gems might be recklessly getting ahead of themselves.