Sgt. Blackitt sets off to give a first aid demonstration at a youth club where trouble is in the air. Jigger Daniels, released from Borstal, is back in town and has a few old scores to settle. Meanwhile Lynch has his own problems. Someone is going around Newtown stealing transistor radios from parked cars, and Barlow is in one of his 'leave no stone unturned' moods.

The suspicions of a canal lock-keeper bring Z-Victor One into contact with the canal community and eventually lead to the investigation of a more serious crime.