Jamie Campbell Bower as Jace, right, and Lilly Collins as Clary contend with unlocking Clary’s memory in the City of Bones in a scene from “The Mortal Instruments: City of Bones.” (Photo credit: Sony Pictures Screen Gems, Rafy)

‘The Mortal Instruments: City of Bones’ a solid start for a promising franchise

Mashing together elements of “Harry Potter” (magic), “Twilight” (romance) and “Supernatural” (Biblical references and plot points), “The Mortal Instruments: City of Bones” manages to represent its source material — a series by Cassandra Clarke of the same name — without too much difficulty. Whether that’s saying “City of Bones” will pick up the mantle of the Potter series or stumble into mediocrity like “Percy Jackson” is the real question. And after the first installment in what seems to be a promising franchise, the answer seems to be somewhat in the middle.

Hewing closely to the book of the same name, “City of Bones” introduces us to the suddenly not-so-normal life of Clary (Lily Collins, “Mirror, Mirror”). A typical teenage girl, her life is quickly flipped upside down when she goes out to a club one night. Seeing someone murdered will do that to a girl. But then again, maybe that’s not what she saw. She has been stressing out over seeing something else: strange symbols all around her (one in particular) that seem to be invisible to everyone else, even her best friend, Simon (Robert Sheehan, “Season of the Witch”). Several overwhelmingly intense segments later, Clary comes to the realization that she is a Shadowhunter: a half-human, half-angel charged with protecting humanity from demons. At about the same time, Clary’s mother (Lena Headey, “300”), a talented Shadowhunter who left her mysterious past behind, has gone missing.

This can’t stand, obviously. To find her mother, Clary teams up with Simon and joins force with the ever-witty, sharply featured Jace (Jamie Campbell Bower, “The Twilight Saga: New Moon”), a Shadowhunter bad boy decked out in leather and weapons.

The quest to find Clary’s mother, however, changes drastically as the Shadowhunters reveal that the true target is the Mortal Cup, one of three divine items given to man from the angel Raziel to the first Shadowhunter. (The other two come into play in later books.) The Mortal Cup is capable of turning humans into Nephilim, the formal name for Shadowhunters. It seems everyone is after the cup, from the Shadowhunters to vampires to demons and everybody in between. The Cup is capable of saving humanity — or destroying it, depending on whose hands it is in.

Clary’s mother is the only person who knew its whereabouts, though Clary may possess that information somewhere in her less-than-accurate memory. It kind of gets a bit more chaotic from here, with Downworlders (vampires, werewolves, the like) joining the fray in roles both hero and villain. (Two particulars stand out: werewolf Luke (Aidan Turner), who served as a surrogate father-figure to Clary in her youth; and Magnus Bane (Godfrey Gao), the high warlock of Brooklyn, who plays a small but important role in all this madness.)

Despite the convulsing plot structure, director Harald Zwart (2010’s “The Karate Kid”) keeps the effects well done and constant, which works in a film about angelic powers. And the chase and fights scenes hold up for the most part (minus the inevitable deus ex machina moments).

The central narrative here proves to be easy to grasp: Clary and Jace fall in love with each other; Simon pines for Clary; and Shadowhunter Alec (Kevin Zegers, “Dawn of the Dead”) has a forbidden crush on Jace. It’s just a whole ordeal of lover’s triangles and unrequited love.

Some downsides: If you haven’t read the books (four sequels, three prequels), you’re going to be lost. There’s a steep learning curve, and some lines and scenes only make sense if you have that background knowledge.

Let’s be honest: While “City of Bones’” cast isn’t Oscar-worthy, it’s leaps and bounds more entertaining than “Twilight’s.” The wit flows freely and the humor is dry and well executed. No one takes anything too seriously, even if this film is a huge career opportunity.

Spellbinding though it’s not, “City of Bones” does what it was meant to do: Introduce us to the world of “The Mortal Instruments.” The more interesting events occur in later books, so let’s hope the team in charge of the sequel, “City of Ashes,” slated for 2014, improves on its weaknesses.

Three angel-powered stars out of five.

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