Melancholy Undercover: The Story of ABBA

Over half a century after their songs were recorded, ABBA's songs still make people the world over dance and sing every day, and their ability to evoke every emotion has made them the ultimate soundtrack to major life events, from birthday parties and weddings to heartbreaks and memorials.

Since interviewing the four members of ABBA for an article in 2013 - at which time the band had not been interviewed for 30 years - a relationship was sparked between writer Jan Gradvall and the band, and he was grant