The late, lamented Joao Kartoshka had this up on his excellent blog, but the link is dead now (does anyone know what happened to Joao himself?).
Anyway, here's what JK wrote:
Serge Gainsbourg (1928 –1991)- Histoire de Melody Nelson(1971) . When driving his Rolls Royce , a middle aged man knocks a 15 year old girl off her bicycle. Naturally, in the world of Gainsbourg, this leads to seduction and romance.
Gainsbourg's 25 year old wife Jane Birkin provided the vocals for Melody, and is also the cover star.Musical director was Jean - Claude Vannier.
Now acknowledged as Gainsbourg's most influential work, the LP was not a commercial success.