As the U.K. blues-rock boom of the late '60s escalated, Fleetwood Mac were in the thick of it with their second album, 'Mr. Wonderful,' which was released in August 1968. Having just put out their debut at the start of the year, the Mac were rolling full steam ahead.

And much like that self-titled first LP, 'Mr. Wonderful' features a mix of blues covers and originals mostly written by guitarists Peter Green and Jeremy Spencer. The rhythm section of drummer Mick Fleetwood and bassist John McVie anchor the music, with the guitarists free to roam where they choose.

Still, there's something missing here. "It was recorded in four days, and it sounds like it," Fleetwood recalled in his autobiography 'Fleetwood: My Life and Adventures in Fleetwood Mac.' "Ragged low-down blues by the seat of the pants," he calls it, and the album kicks off with a fiery example: Green's 'Stop Messin Round,' which picks up where the debut left off but with one difference. Producer Mike Heron decided to bring in horns and a piano player to augment the band's naturally raw sound. (The pianist, by the way, was Christine Perfect, who later became Christine McVie, on loan from the band Chicken Shack.)

The band's take on down-and-out blues continues in varying degrees throughout 'Mr. Wonderful.' The bluesy stomp of Elmore James' 'Dust My Broom' gets it right, with a raw vocal performance and some ace slide-guitar playing by Spencer. But Green's 'Love That Burns' includes a horn arrangement that dilutes the soul-searing blues the band could be so good at and ultimately distracts from the desperation at hand.

Still, the horns and piano occasionally add a sweet jazzy flavor to the mix. The entire album sounds homemade, which works both for and against it in the end. Songs like 'If You Be My Baby' and 'Lazy Poker Blues' stomp in brash fashion, while 'Evenin' Boogie' features a solid jump blues with excellent horns. And the closing track, 'Tryin' So Hard to Forget,' is stripped bare, with only guitar, vocal and harmonica. It's the purest blues on the album and a highlight, basking in its haunting darkness.

Curiously, even with all of the traditional blues sounds found on 'Mr. Wonderful,' the album was preceded by one of Fleetwood Mac's most significant singles, 'Black Magic Woman,' a non-LP track that revealed their versatility. Likewise, they followed 'Mr. Wonderful' with two more landmark hit singles, 'Albatross' and 'Man of the World,' which steer away from the blues while still using the music as a jumping-off point. A sign of things to come.

Listen to Fleetwood Mac's 'Mr. Wonderful'

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