Fleetwood Mac was once a triumph of British blues before the more pop-leaning Lindsey Buckingham and Stevie Nicks entered the picture.

The group was formed in 1967 by guitarist Peter Green, drummer Mick Fleetwood and bassist John McVie, all of whom had recently fled from John Mayall's Bluesbreakers. They added guitarist Jeremy Spencer to the fold soon after.

At this point, they were deeply indebted to the likes of Elmore James and Robert Johnson. Their first two albums – Fleetwood Mac and Mr. Wonderful, both from 1968 – adhere to a straightforward blues approach, straying very little from formula. But by the time their third album, Then Play On, arrived in September 1969, things were beginning to steer toward more interesting directions.

READ MORE: Top 10 Peter Green Fleetwood Mac Songs

Fleetwood Mac took their basic blues template and added more to the mix. The arrival of guitarist Danny Kirwan gave another dimension to their sound, but the evolving writing styles of both Green and Kirwan would also lift things out of the tried and true.

Then Play On kicks off with the ruminating blues stride "Coming Your Way." Written by Kirwan, the song uses the blues as a jumping-off point, but weaves in an ethereal quality – a combination of Green's lead guitar and Fleetwood's rumbling percussion that makes for a perfect album opener. Green's haunting "Closing My Eyes" sneaks in next, with nothing but vocals and guitars. It's a dark song that evokes the soul of the blues without relying on the form.

Kirwan's "When You Say" goes the acoustic route, while Green's "Show Biz Blues" turns into a country-blues raver featuring some great acoustic slide guitar. On the instrumental "Underway," Green gets to cut loose with some beautiful lead work that drifts and lifts itself higher and higher as the song moves on.

Side two begins with one of the band's most beautiful Mac songs, Kirwan's "Although the Sun Is Shining," a short but sweet acoustic number. The next track, "Rattlesnake Shake," takes an opposite approach. This is blues but far removed from the traditional route. Just as Cream twisted the music into other shapes, Fleetwood Mac created something utterly new from old forms. The song was a centerpiece of their live shows at the time, sometimes carrying on for nearly 30 minutes.

Listen to Fleetwood Mac's 'Rattlesnake Shake'

First Hints of Peter Green's Troubles

"My Dream" became an instrumental showcase for Kirwan, who also penned "Like Crying," an Everly Brothers-style song that sets up a duet with Green. "Before the Beginning" ends the original LP as it started, with haunting guitars and vocals, ushering listeners out the same way they were invited in. It's another fine Green composition that hints at the inner turmoil that would eventually be his undoing.

Rolling Stone didn't think too much of Then Play On at the time, calling it "slow and wandering. ... On this album, they fall flat on their faces." True, the record has slow spots – too many mid-tempo songs and instrumentals tend to take away from the flow – but in retrospect, Then Play On shows the band in search of a new identity. That remains one of its most intriguing artifacts.

Even so, that's not the entire story of this chapter in the band's long career. Two significant singles were released after the album came out: "Oh Well" and "The Green Manalishi (With the Two Prong Crown)." The first arrived shortly after the LP and was later added to later U.S. pressings of Then Play On. It remains one of Fleetwood Mac's greatest songs. Its monster riff alone is a head-turner, but the barn-burning fury the band delivers is mind-boggling.

Green's autobiographical lyrics take things to another level: "Now, when I talked to God I knew he'd understand / He said, 'Stick by me and I'll be your guiding hand / But don't ask me what I think of you / I might not give the answer that you want me to.'" "Oh Well" climbed to No. 2 in the U.K. and remained a part of Fleetwood Mac's live set for decades.

Listen to Fleetwood Mac's 'Green Manalishi'

One Final Triumph Before a Departure

On the other hand, "The Green Manalishi (With the Two Prong Crown)" is where it all ends as Green's final recording with the band. This is where his vision of the blues and the world in general comes into evil and haunting focus. Green's heavy LSD use comes through in both sound and words.

By the final coda, Green has essentially lost his mind – primal scream therapy set to a menacing blues dirge, if you will. Not since Del Shannon, another troubled soul, issued "Keep Searchin' (We'll Follow the Sun)" in 1964 had anyone sounded this unhinged. ("Green Manalishi" was given a second life when Judas Priest recorded a more straightforward version a decade later.)

Then Play On helped to establish Fleetwood Mac in the U.S., gaining a foothold in the underground scene. Green would soon leave the band under mysterious circumstances involving religion and drugs. Fleetwood Mac returned with a series of transitional albums in the early '70s before becoming one of the biggest bands in the world when two Americans joined for another chapter in their awesome career.

Fleetwood Mac Albums Ranked

It's easy to focus on Lindsey Buckingham and Stevie Nicks when considering a list of Fleetwood Mac albums, but the band's legacy extends well beyond that.

Gallery Credit: Nick DeRiso

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