Unpleasant things are going on in an exclusive school for girls - things like murder...

Late one night, two teachers investigate a mysterious flashing light in the sports pavilion, while the rest of the school sleeps. There, among the lacrosse sticks, they stumble upon the body of the unpopular games mistress - shot through the heart from point blank range.

The school is thrown into chaos when the `cat' strikes again. Unfortunately, schoolgirl Julia Upjohn knows too much. In particular, she knows that without Hercule Poirot's help, she will be the next victim...