A school chemistry lab and some unsupervised senior students, MacPherson and Jenkins are preparing a prank on one of their own... However, a friend of theirs, a very tall boy called Stephen Franklin is worried if they have calculated the amount that the others are pouring into a test tube... Paignton, a rather obnoxious Billy Bunter type victim of the prank gets a face full of test tube fragments and scalding liquid as it explodes in his face. The boys watch in horror as Paignton screams and screams and screams.... (thetvdb.com)