Everything pointed to Ben the three-pronged knife, the scratches on his face. And why was he out and about that dark night?Penelope Thanatopoulos doesn't like Benjamin Thorpe but she is shocked when he is suspected of attacking Kevin Friend at the zoo where they are on work experience. Who stabbed Kevin and threw him into the seal pool?Penelope makes it her business to find out.KERRY GREENWOOD has written a chilling mystery for younger readers in The Three-Pronged Dagger.