When Daisy Wells and Hazel Wong set up their very own deadly secret detective agency at Deepdean School for Girls, they struggle to find any truly exciting mysteries to investigate. But then Hazel discovers the Science Mistress, Miss Bell, lying dead in the Gym. She thinks it must all have been a terrible accident - but when she and Daisy return five minutes later, the body has disappeared. Now the girls know a murder must have taken place - and there's more than one person at Deepdean with a motive.