Gallagher Girls: I'd Tell You I Love You, But Then I'd Have To Kill You : Book 1 by Ally Carter

Gallagher Academy might claim to be a school for geniuses - but it's really a school for spies. Cammie Morgan is fluent in fourteen languages and capable of killing a man in seven different ways (three of which involve a piece of uncooked spaghetti). But the one thing the Gallagher Academy hasn't prepared her for is what to do when she falls for an ordinary boy who thinks she's an ordinary girl.