“Isabelle and Sebastian? Hardly. Sebastian’s a nice guy – Isabelle only likes dating thoroughly inappropriate boys our parents will hate. Mundanes, Downworlders, petty crooks…”
“Thanks,” Simon said. “I’m glad to be classed with the criminal element.”

“But that was Isabelle — if there was a boy around and blame that needed to be pinned on someone, Isabelle would pin it on him”

“"Where's Simon?" Clary interrupted.
Isabelle wobbled. "He's a rat," she said darkly.
"Did he do something to you?" Alec was full of brotherly concern. "Did he touch you? If he tried anything-"
"No, Alec," Isabelle said irritably. "Not like that. He's a rat"”

“Really? Are you going to ask him to be your partner?" Isabelle asked. "It's like cotillion, this partners business, except with killing."
"So, exactly like a cotillion," said Simon.”

“Simon bristled. She wasn’t his Isabelle, not anymore. He wondered if she ever truly had been. Isabelle didn’t seem like the type of girl to belong to someone. It was one of the things he liked best about her.”

“Isabelle!” Simon called. “Stop throwing clothes at me! Just because you’re a Shadowhunter and I’m a vampire doesn’t mean we can never happen. Our love is forbidden like the love of a shark and a—and a shark hunter. But that’s what makes it special.”

“He looks," Simon had once said to Isabelle, "like he's thinking about something deep and meaningful, but if you ask him what it is, he'll punch you in the face.”

“I could give you a thiught sheath to put that in,"Isabelle offered. "I got tons."
"CERTAINLY NOT," said Simon.
Clary shot him an irritated look. "Thanks, but I'm not really a thigh sheath kind of girl,"
-pg. 214”

“They are a very great boon to mankind, dentists,’ said Isabel. ‘And I’m not sure that we are grateful enough to them. I’m not sure that we even bother to thank them.’ She paused. Were there any statues of dentists? She thought not. And yet there should be.”

“I need Jace,” said Sebastian. “But in his heart, he’s not like me. Butare.”