Speak False Truths

"Look, it's easy to outsmart a werewolf or a vampire," Jace said. "They're no smarter than anyone else. But faeries live for hundreds of years and they're as cunning as snakes. They can't lie, but they love to engage in creative truth-telling. They'll find out whatever it is you want most in the world and give it to you-with a sting in the tail of the gift that will make you regret you ever wanted it in the first place."
He sighed. "They're not really about helping people. More about harm disguised as help."