With an acclaimed second album under its belt, a new deal with CBS Records, and a recording budget that seemed astronomical to the practically broke band, Judas Priest went into the Sin After Sin sessions in early 1977 with the intent on making an even bigger impression than the revelatory Sad Wings Of Destiny did the year before. Only despite the increased luxury afforded the band, it was a bumpier ride than anticipated. CBS suggested the band hire Deep Purple bassist Roger Glover as producer, based on his work on Nazareth’s scorching cover of Joni Mitchell’s “This Flight Tonight,” but the idea was scrapped after the personalities couldn’t gel, the band members preferring to produce the album themselves.

Weeks later, however, Judas Priest found itself in a bind. Drummer Alan Moore abruptly quit, leaving the band in desperate need of a replacement with only six days of booked studio time left at the Who’s Ramport Studios. A phone call was made, fences were mended, and Glover was brought in to expedite the recording process. He brought in teenaged session drumming phenom Simon Phillips, who then was best known for his work with Brian Eno’s and Phil Manzanera’s post-Roxy Music project 801. The album was completed in five days, and despite a couple of missteps — one minor, one much worse — the resulting Sin After Sin continued the momentum set by Sad Wings Of Destiny.

By 1977 Judas Priest was quickly developing its own sound, and while not a stone classic in the vein of Sad Wings Of Destiny and 1978’s Stained Class, Sin After Sin is a crucial transitional album in the Priest discography, and its best moments are spectacular. The band was evolving more and more, becoming faster and heavier, and this album is at its very best the more extreme it gets. Three tracks in particular are especially prescient. Opening song “Sinner” is startlingly aggressive compared to the previous two albums, Rob Halford adopting a menacing snarl that would quickly one of the most important parts of his vast vocal arsenal, the song boasting a towering chorus propelled by Phillips’s thunderous double-kick beats. “Let Us Prey/Call For The Priests” is the fastest Priest song to date, Phillips echoing the rampaging pace of Deep Purple’s “Fireball” and subsequently anticipating the initial wave of thrash metal five years later. “Dissident Aggressor,” meanwhile, remains one of the heaviest songs the band has ever recorded, three minutes of churning, primal power featuring a striking, rumbling rhythm riff by Tipton and Downing and a classic vocal performance by Halford.

Just as important as the extremity of those three tracks is the streamlined hard rocker “Starbreaker,” whose modern, hard-driving groove would anticipate the band’s turn towards a more commercially accessible style two years later. Also of note is the galloping, bombastic cover of Joan Baez’s 1975 folk tune “Diamonds & Rust,” which was originally recorded during the Sad Wings sessions and given a sharper re-recording on the suggestion of Glover, who felt the album needed a good mainstream-friendly single, which, as it would happen, was a smart move.

“Raw Deal” is a strange curiosity, a bluesy rocker reminiscent of Rocka Rolla, with lyrics by Halford that in retrospect seem to hint at his homosexuality: “All eyes hit me as I walked into the bar / And seeing other guys were fooling with the denim dudes / A couple cards played rough stuff, New York, Fire Island.” “Last Rose Of Summer” is a decent, passable albeit unspectacular progressive rock ballad, but although that song is an odd fit, even worse is “Here Come The Tears,” a woeful ballad that cranks the emotional histrionics full tilt and doesn’t let up until the listener is cringing with embarrassment.

Thankfully the good far outweighs the mediocre, and audiences were quick to pick up on the album’s strengths, as it charted at number 23 in the UK. Although Sin After Sin made no impact in North America, the band’s affiliation with CBS afforded it a chance to tour America for the first time, supporting Foreigner, REO Speedwagon, and most notably, Led Zeppelin. Despite a drumming performance that would influence many, Phillips could not commit to being a full-time member, but Glover saved Priest’s bacon one more time, suggesting they hire Les Binks, who played on his solo album The Butterfly Ball And The Grasshopper’s Feast. Not only was he capable of replicating Phillips’ ferocious double-kick beats, but Binks would play on the next three Priest albums, which would go on to become three of the most revered titles in the band’s discography. Big things lay ahead.