Strategically sited throughout London Transport's railway system, at immediate call, are Power Signal Linemen, ready to put right any faults that may occur. The film, which is part of London Transport's training course for power signal linemen, shows a possible fault, and how the lineman makes repairs. It emphasises the conditions of urgency and stress under which a lineman must work, and the patient, methodical skill he must nevertheless bring to any problem if it is to be solved successfully as well as speedily.