Laurels are Poison — Gladys Mitchell

The witchlike psychologist and detective Mrs Bradley takes up the position of warden at a girl's college in order to investigate the ominous disappearance of her predecessor. Her arrival coincides with a series of sinister practical jokes - a student's hair is hacked off, clothes are slashed, then the cook's body is discovered in a river near the college. With the help of her sub-warden and a trio of intrepid students, Mrs Bradley hunts down the culprit.