Narinder Dhami 
Bang Bang You’re Dead 

When a mysterious gunman takes a class hostage, the rest of Mia’s school is evacuated. But Mia is determined to stay behind. She knows it’s a life or death situation but there’s something she fears more than dying. Mia thinks she might know who the gunman is, and, if she’s right, then she may be the only one who can save her schoolmates…