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 head from point-blank range. The school is thrown into chaos when the "cat" strikes again. Unfortunately, schoolgirl Julie Upjohn knows too much. In particular, she knows that without Hercule Poirot's help she will be the next victim.