It uses the Thames Tunnel designed by Sir Marc Isambard Kingdom Brunel, and completed in 1843, to pass under the river.
The line was electrified in 1913 and was initially worked with Metropolitan Railway saloon stock.
It passed to London Transport in 1933 and saw a wide variety of rolling stock during its time as part of the Underground, including F stock, Q stock, CO/CP stock, 1938 tube stock, A stock in various liveries and D stock.
All appear in this production as well as a tour of the line using London Transport Museum's preserved 1938 tube stock just before closure in 2007, and some last day views.
In the second part we see the line reopened as part of the London Overground network.
There are scenes taken on the opening day when a limited service ran from Dalston Junction to New Cross and New Cross Gate.
The line was extended northwards via Shoreditch High Street along the embankment used by the former line into Broad Street.
From May 2010 the line was further extended southwards, from New Cross Gate to West Croydon and Crystal Palace, over Network Rail's tracks, and operation on these lines is covered in detail.
To work the line as part of the Overground, a fleet of new 4-car class 378 EMUs has been built and a new depot constructed at New Cross Gate.
The stations have been transferred to London Overground control and given new signage.
Where the ELL shares tracks, we see trains operated by Thameslink, Southern and South Eastern.