City of Bones (The Mortal Instruments Trilogy) by Cassandra Clare

What's on the back of the book:
Clary Fray is seeing things: vampires in Brooklyn and werewolves in Manhattan. Irresistably drawn towards a group of sexy demon hunters, Clary encounters the dark side of New York City - and the dangers of forbidden love.

A piece from the book:
Clary stepped forward to touch Jace's arm, say something, anything - what did you say to someone who'd just seen his father's killers? Her hesitation turned out not to matter; Jace shrugged her touch off as if it stung. "We should go," he said, stalking out of the office and into the living room. Clary and Simon hurried after him. "We don't know when Luke might come back."
They left through the back entrance, Jace using his stele to lock up behind them, and made their way out onto the silent street. The moon hung like a locket over the city, casting pearly reflections on the water of the East River. The distant hum of cars going by over the Williamsburg Bridge filled the humid air with a sound like beating wings. Simon said, "Does anyone want to tell me where we're going?"
"To the L train," said Jace calmly.
"You've got to be kidding me," Simon said, blinking. "Demon slayers take the subway?"
"It's faster than driving."
"I thought it'd be something cooler, like a van with DEATH TO DEMONS painted on the outside, or . . . "
Jace didn't even bother to interrupt. Clary shot Jace a sideways look. Sometimes, when Jocelyn was really angry about something or was in one of her upset moods, she would get what Clary called "scary-calm." It was a calm that made Clary think of the deceptive hard sheen of ice just before it cracked under your weight. Jace was scary-calm. His face was expressionless, but something burned at the backs of his tawny eyes.
"Simon," she said. "Enough."
Simon shot her a look as if to say, Whose side are you on? but Clary ignored him. She was still watching Jace as they turned onto Kent Avenue. The lights of the bridge behind them lit his hair to an unlikely halo. She wondered if it was wrong that she was glad in some way that the men who'd taken her mother were the same men who'd killed Jace's father all those years ago. For now, at least, he'd have to help her find Jocelyn, whether he wanted to or not. For now, at least, he couldn't leave her alone.