Red Handed

2007 book by Gena Showalter. Phoenix Germaine has been trying to earn back her mother's trust after going into rehab and kicking Onadyn -- the drug of choice for New Chicago teens. But when a party in the woods turns into an all-out battle with the most ferocious aliens Phoenix has never seen, she's brought home in what appears to be an Onadyn-induced state. Hello, reform school.

Except, what her mother doesn't know is that Phoenix has just been recruited to join the elite Alien Investigation and Removal agency, where she'll learn to fight dirty, track hard, and destroy the enemy. Her professional training will be rigorous and dangerous, and the fact that one of her instructors is Ryan Stone -- the drop-dead gorgeous, nineteen-year-old agent she met in the woods that night -- doesn't make things any easier.

Tropes:

 * Aliens Are Bastards: For the most part.
 * Alien Invasion: Happened long before the book started.
 * Alpha Bitch: Allison Stone
 * Awesome McCoolname: Phoenix Germaine, Ryan Stone
 * Catgirl: Kitten, though strictly speaking she is an alien.
 * Fantastic Drug: Onadyn, which was made for aliens who couldn't handle oxygen but humans abuse it to get high.
 * Fantastic Racism: Against aliens or Outers.
 * Government Agency of Fiction: Alien Investigation and Removal agency, or A.I.R.
 * Humanoid Aliens: Most aliens described fall into this.
 * Kidnapped By an Ally:
 * The Masquerade: The public doesn't know the truth about predatory aliens.
 * Military School / Spy School: The Alien Investigation and Removal agency school is a combination of the two.
 * New Neo City: New Chicago
 * Ray Gun: The trainees learn how to use one.
 * Teacher-Student Romance:.
 * Teen Superspy: Phoenix becomes one of these.
 * Twenty Minutes Into the Future: Probably closer to just being "The Future". Apparently aliens have been living among humans for 70 years.
 * Wild Teen Party: The opening