The Mortal Instruments: City of Bones might seem like the next Twilight Saga or The Hunger Games, but author Cassandra Clare promises it's a different breed of story. She was at WonderCon in Anaheim to help represent the movie during Sony Pictures' panel, and told Comic Book Resources prior to the presentation that there's going to be enough action in City of Bones to keep male fans happy.

"I have a lot of boy readers and they love it because there's a ton of action,” she said. “There's a lot of people's heads getting chopped off, there's a lot of monsters. It is really gritty and dark. One of the fantastic things about the young-adult category is that it blends millions of different genres. Twilight is romance to me. The Hunger Games is a dystopian science fiction. This is classic urban fantasy. It's really a different thing."

That means people shouldn't expect the romance between Lily Collins' character Clary Fray and Jamie Campbell Bower's Jace Wayland to be the main focus of the film. "The love story is romantic, it's there, it's the B plot, but the A plot is about this girl discovering who she is and becoming involved in this magic world and this story of demons and monsters and protecting the world from these sinister forces," Clare said. "I'm excited about it."

City of Bones has assembled an impressive cast, including Game of Thrones star Lena Headey and The Tudors' Jonathan Rhys Meyers. Clare was involved in casting the film, something she said she feels "really lucky" about.

The movie features werewolves, vampires, warlocks and demons, but Clare said they aren't the romantic sort of creatures. "It's certainly very different from Twilight. The vampires are monsters. They're dangerous, dangerous monsters," she said. "There's demons who are completely evil and floating around the middle is this race that they call the Downworlders that are warlocks, fairies, vampires, werewolves. What I like about them is they're incredibly ambiguous figures. They can do good, they can do evil. They have their own free will."

Those creatures haven't been teased much in the promotion for City of Bones, but Clare said director Harald Zwart created them primarily through practical effects. She said she's a fan of that style of filmmaking, and that it was "really cool" to see her creations brought to life on set.

"The Silent Brothers are the sort of creepy monks of the Shadowhunter world. Their eyes are sewn shut, their lips are sewn shut, so they were on set and they had the prosthetic makeup," she recalled. "We had to break for lunch and there they all are and their lips are sewn shut so they're drinking out of juice boxes that are stuck in the side of their mouths and I'm like, this is so funny. I'm never going to forget it."

In addition to The Mortal Instruments trilogy, Clare has also written a sequel trilogy (the final book will be released in March 2014), a prequel trilogy set during Victorian England called The Infernal Devices, and she is planning a spinoff series of short stories following the character of Magnus Bane. That means there's plenty of material if Screen Gems decides to make more Mortal Instruments films.

"It's a big sprawly world. It's got a lot of stuff in it. If this one does well, yes, [more films] until the dawn of time, which would be great and exciting," Clare said. "It's fun because there's just so much there so being able to be involved in the production meant that I could kind of tell them stuff that was going to happen in upcoming books and stuff that was behind the scenes of the first book, so there are little nods no the fans about things that are going to happen later, which is great."

The Mortal Instruments: City of Bones is due in theaters Aug. 23.