Student Martin Clarke has been stabbed and PCs Roger Valentine and Dan Casper go to the school to investigate. At St Hugh’s Hospital, Martin’s angry father Carl announces that Wayne Tindle is the attacker.

Meanwhile, at the school, Sergeant June Ackland and Pc Tony Stamp interrogate Wayne but when another student, Tom Ryan, is interviewed, he admits to stabbing Martin – and the knife used comes back from forensics covered in his prints.

Back at Sun Hill, Inspector Gina Gold tells Smithy that they must find Jimmy Collins (Leslie Grantham), who hasn’t returned to his open prison. When they go round to Jimmy’s house, they see him driving off. Jimmy’s blood-soaked car is found – without Jimmy – and June and Gina learn that his blood is on the knife used to stab Martin. It turns out that Jimmy and Tom Ryan’s late father, Bob, were best friends.

Gina sets off to visits Tom’s mum, Maria, to find out where Jimmy is. Smithy learns that Jimmy’s on his way to see Maria and gets on the police radio to warn Gina. But it’s too late, Jimmy walks in wielding a knife, ordering Gina not to answer Smithy’s call…