It’s 1979, and ABBA are one of the world’s most famous bands. But beneath their successful surface, things are changing.In Episode 3, Sara Cox follows the band to the peak of their career. As ABBA release some of their most iconic and sophisticated music, their personal relationships come under incredible strain. The band play on - but how long can they really last?Through the BBC Archive and brand new interviews, we chronicle the beginning of the end for the masters of the scene.