Two tennis players meet in the ladies semi-final of Wimbledon. One of them, Valery Middleton, is older, more experienced and the clear favourite. However, she is killed during a break in play, and it is not clear who did it.
Aliens have landed in the school! They look and behave like people. The only way to discover them is to listen carefully to what they say. Aliens always make mistakes when they ask questions in English!