(Sorry for being a bit slow on the update.)
"Eagle", by ABBA. By the time of "ABBA: The Album" I had disembarked from the ABBA cruise ship and was about to board the Post-Punk Express. So I missed hearing the bulk of ABBA's "mature" work, until many years later, because of course you couldn't be a Man In Black and also an ABBA fan (at least publicly, so it was best not to do it at all).
And so I come to "Eagle", via its appearance on Lindstrom's "FACT 100" mix, with fresh ears. And what do I hear? All of the bigness you expect from a great ABBA song: outsize arrangements; outsize vocal harmonies; outsize underlying psychodrama; outsize ambition; outsize success. But something else: a pre-echo of the New Pop that would grip the world four or five years later. In fact, there is an element buried in this song that is so close to the Human League's "Don't You Want Me" that ABBA's lawyers must have pricked up an ear or two. (Not only that, but the song's opening also prefigures the music of Studio, and others of the (for want of better descriptions) nu-Balearica school. They really did have all bases covered.)