Using stills and archive film, kindly supplied by London's Transport Museum, we see the City and South London Railway's distinctive rolling stock being pulled by diminutive electric locomotives.
The massive task of enlarging the original tunnels to take standard size tube rolling stock, is featured.
The story also covers the Hampstead Tube, and the various extensions and links that were built to create today's line.
The isolated Great Northern and City Railway, between Moorgate and Finsbury Park, became part of the Northern Line in 1939 and is seen in operation in its latter days.
The wide variety of rolling stock that has operated on the line is seen, together with the 1995 stock under construction at the Alstom factory in Birmingham.
The remainder of this programme gives detailed coverage of the present day scene, including interesting aspects of infrastructure and station architecture.