The first time I traveled to Sweden, it was to interview Opeth. I’d interviewed the band’s leader, Mikael Åkerfeldt, once before, in 2003, in between the release of their extremely heavy Deliverance and its quieter companion, Damnation, and I’d been a fan ever since. In 2008, I was the editor of Metal Edge magazine, and Roadrunner Records flew me and a writer from Decibel to Stockholm to hear the band’s forthcoming album, Watershed, and interview all the members. (The trip was in January or February, as I recall; mid-2008 was about the last time record labels were willing or able to fund international press junkets. Metal Edge shut its doors in February 2009.)

Watershed, it turned out, marked the end of Opeth‘s existence as a metal band. Their next release, 2011’s Heritage, was a hard rock album, not a metal album, and its opening title track was an instrumental piece for grand piano and upright bass. Even its heaviest songs, “The Devil’s Orchard” and “Slither,” and the like, had a driving groove, moving beyond the death metal avalanche of their previous material to let the rhythms shift and breathe; drummer Martin Axenrot, who had joined on Watershed, proved to be capable of slinky swing as well as jackhammering hard rock.

On Pale Communion, the band further synthesized their evolving prog-rock style. The organs and Mellotrons were often louder than the guitars, pounding out riffs that owed a lot to early ’70s Deep Purple but even more to modern-day Uriah Heep. They also indulged a heretofore hidden taste for funky fusion on the instrumental “Goblin,” named for the Italian band of the same name best known for soundtracking all the best Dario Argento movies, and went weepily epic on “Voice of Treason” and “Faith in Others,” the latter featuring some lushly beautiful string arrangements.

After Pale Communion, Opeth left Roadrunner and formed their own label, distributed through Nuclear Blast. Their next studio release, 2016’s Sorceress, was a little bit of a hodgepodge; it had some more jazz-funk prog-rock songs and a couple of acoustic ballads and interludes, but also featured two of the heaviest tracks they’d recorded in quite a while, “The Wilde Flowers” and “Chrysalis.” The deluxe version came with a second disc that included three live tracks, recorded with an orchestra, that justified the purchase all on their own.

A vocal contingent of Opeth “fans” have griped continuously since Åkerfeldt first took the band down this prog path. Every time the band puts out an album, they post comments asking when the death metal growls of their first nine albums are coming back. They’re not, and the band’s latest release, In Cauda Venenum, is likely to piss them off even more. Not only is it the band’s most completely progged-out album, it’s not even in English! Åkerfeldt decided that for the band’s 13th studio album, he would sing everything in his native Swedish. As someone who’s been studying the language for several years, I was immediately thrilled by this prospect. (He did ultimately record an English-language version, but has stated in multiple interviews that it was an afterthought and a concession, and that the Swedish version is the “real” version.)

The album opens with a shortish intro track, as Heritage and Sorceress did (Pale Communion dove right in with a full song). This one, “Livets Trädgård,” which translates to “the garden of life,” features wordless choral vocals that sound like they’re being played on a Mellotron. Gradually, synths come pulsing in out of deep space, for an effect that’s half Popol Vuh, half Tangerine Dream. Then we get some recordings of what sound like children playing on a schoolyard, and a small child speaking to someone, and then the first song proper, “Svekets Prins” (“the prince of deceit”), comes roaring in.

Most of the songs on ICV are much heavier than those on the previous three albums, but it’s a heaviness that, again, sounds a lot like present-day Uriah Heep or mid ’80s Deep Purple (“Under the Gun,” “Knocking at Your Back Door”), especially given the use of strings and the way keyboardist Joakim Svalberg dominates the mix. “Hjärtat Vet Vad Handen Gör” (“the heart knows what the hand does”) speeds down the road, propelled by a massive Martin Lopez bass line and thundering drums from Axenrot. There are some lovely ballads, though, like “Minnets Yta” (“the memory’s surface”) and “Banemannen” (“the slayer”), on which the changes in Åkerfeldt’s voice brought about by singing in Swedish really become obvious. The language has a much different innate melody from English, a little more singsong, and it pushes him into his upper vocal register. He’s a softer, more sensitive vocalist in Swedish, and he compensates for that by allowing the backing vocals — and strings on some tracks, like “De Närmast Sörjande” (“they are mourning the most”) — to do a lot of heavy lifting.

A major part of Opeth‘s appeal is that they continually evolve. This album poses a challenge to listeners; it’s the most accomplished and assured of their “prog era” records, at the same time that it’s a return to heaviness not seen since Watershed. The English-language version could please more longtime fans than anything they’ve done in years, but Åkerfeldt wants people to hear it in Swedish. For his sake, I hope people welcome In Cauda Venenum, because it’s incredible, easily one of the best rock records I’ve heard all year.