The opening titles are followed by a sequence of László Moholy-Nagy's kinetic light display sculpture. The commentary introduces the subject of applied science and the importance of research to modern society. Unnamed technicians at the GPO's Research Laboratories, at Dollis Hill in North London, test "specimen telephones for the dial system". Volume, durability and sensitivity of receivers are tested.

The planning of the new exchanges needed across the country as the system is converted from manual to automatic exchanges. An explanation of the way statistics of telephone use are employed by planners to establish the necessary size of different exchanges. Draughtsmen are seen designing the buildings. The building of a new telephone exchange in the City of London is shown.

The film celebrates the process of modernisation in the context of "modern business and modern commerce"; speaking of the construction of this exchange, the commentary announces that progress demands improved communications, and proclaims the new exchange as "the nerve centre of a new system of communication". Masses of underground telephone cables are shown emerging, in lead-sheathed bundles, into the basement of the exchange building. The cables are followed into the frames of electromagnetic switches, which are described as "the answer of the mathematician and the engineer to the modern demands for speed and organisation". Engineers complete an installation. A brief instructional sequence explains the link between the dialled numbers and the operation of the exchange. A man dials via a manual operator then via an automated exchange. A sequence explains the automatic alarms that enable faults to be reported. A final sequence stresses the importance of modern telephony to the effective operation of a city such as London.