Musical taxonomy is an interesting thing. Genres twist and mingle like gnarled branches, running parallel to one another but being careful not to touch.

Take for instance, metal and emo. Despite their affinity for sonic catharsis and death, there’s very little camaraderie  between the two. However, they each have a symbiotic relationship with post rock. Metal and post rock have fed off of eachother for decades, with bands like ISIS and Mogwai liberally reaching across the branch. Similarly, emo and post rock have much more in common than loud/soft dynamics and precious sonic elements. Bands like American Football and The Appleseed Cast have been mixing the two for two decades. And yet, metal and emo have remained distinctly distant despite this shared commonality.

But on Isolation Ritual, Boston’s HarborLights bridge the gap in a way that never feels incongruous.

Strictly speaking, HarborLights is a post rock band. A quick perusal of their Bandcamp page shows a string of albums and EPs stretching back to 2012, the earliest landing in the center of what would be considered post rock. I haven’t had the chance to listen to the rest of the material in the interim to trace the twists and turns that led them to Isolation Ritual, but I don’t need to. It stands on its own as a revelation.

Guitars vary from glittering clean riffs and fiery atmospherics. Drums crash and pound with the fury of bands like Pelican and Russian Circles. And, odd for a post rock album, five of the ten songs have vocals—and not like textural, Sigur Rós style vocals either: these are proper songs, with verses and choruses.

And unexpectedly, Matthew Right’s voice sounds much more like that of an emo or post hardcore frontman (you want to talk about some gnarled branches!) than a metal vocalist. Don’t think that to mean he sounds whiny—absolutely not. His voice is closer to an upper baritone, and barring the screamed vocals on the closer, he never really pushes his voice that hard. And it works.

Opener “Hold The Dark” begins the record with delay-drenched guitars and a rim-driven drumbeat behind Right’s verses, before exploding into a firestorm of a chorus. “Eternal Return” abandons any pretense of building to a climax and bursts out of the gate with a heavy guitar line with an almost hardcore punk drum beat, quieting down in the middle sections before bursting again. “Skinwalker” is one of the most impressive instrumentals on the album, pairing atmospheric guitars and elastic riffs with drummer Jordan Rodriguez’s agile rhythmic shifts, moving from heavy metal riffs to an almost Latin shuffle.

“From Virtue (Sacrament)” is one of the strongest songs on the album, pulling the closest to traditional songwriting. It doesn’t hit the same cathartic explosions as many of the other tracks, instead they weave intertwining rhythmic lines together to great effect. That track collapses into “A Stable Mind,” a meditative track that closes the A side an acoustic guitar and harmonic picks.

The B-side opens with “A Year Without Summer,” a song that plays to the soft-loud dynamic as devotedly as possible. The verses feature plaintive strums over Right’s cooing voice while the chorus pounds with every cymbal fuzz pedal they can muster. “Ego Ideal” is a near ballad, its somber guitars and lamenting vocals driven along by intricate drum patterns until the climactic final moments. “…And Hell Followed” is textbook post metal with a spooky minor key guitar riff that wouldn’t feel out of place on a Neurosis record.

“The Unbearable Lightness of Being” closes the record with one of the best performances of the year. Throughout its mercurial eight minute runtime, it shifts from grooving post rock (just listen to that harmonized guitar fill!) to explosive walls of guitar noise to swelling ambience, tensely building to a full on heavy metal onslaught, complete with screamed vocals.

Mixing genres can often feel gimmicky. Certain formulas might work for a song or two, or even a full EP, but they run dry across a full length. But nothing about Isolation Ritual feels cheap or hackneyed. Rather, this record is consistently fresh and inventive, surprising and satisfying at every turn.