There's something terrifyingly beautiful about Bohren & Der Club Of Gore's music, most obviously the sheer unhurried lethargy of it. Each piece moves slower than hell, meditating at the sort of pace the 20th century's communication explosion almost killed off. Each Bohren release evokes the sedate momentum of ancient sea travel, snailing forward through barren landscapes, perhaps unknowingly in circles, constantly tempting one to ask, "have we been here before?"

The story of the band's progress has been as persistently sedate as the music itself, with the now-signature sound of Christoph Clöser's tenor sax not actually entering the group until some eight years after their formation and two monolithic albums of guitar-led imaginary midnight movie soundtracks in 1994 and 1995. The group's loosely-definable second phase following the departure of Reiner Henseleit and his guitar and the introduction of Clöser and his sax seemingly came to something of a conclusion with the 'Beileid' mini-album in 2011, with Mike Patton even joining them to croon across an unrecognisable cover of 'Catch My Heart' by 80s German metallers Warlock. An approximation of light had begun to appear behind the curtains of the long-abandoned jazz club where Bohren & Der Club Of Gore have been living for two decades now, with semblances of major keys and the distant-memory of the bright outside world languidly returning since 2008's Dolores. Their progress having slowed to a near-standstill, the group take a sideways step with Piano Nights and continue their slow march towards the eternal embrace of the grave, albeit with something of a resigned grin of acceptance across their faces.

Supposedly inspired by a lonesome moment behind a grand piano in Moscow, the eponymous instrument is the most notable addition to the group's gentle arsenal here, pushing aside the warmth of Bohren's mainstay Fender Rhodes, but leaving the synth choirs, organs, vibes and breathtakingly restrained rhythm section of bassist Robin Rodenberg and drummer Thorsten Benning utterly intact. Clöser's saxaphone seems to have subtly undergone its own infinitesimal metamorphosis, eroding away at the fleshy vibratos and breathy linger to leave a coldly hollow and synthetic core. It resultantly sounds its very least human, as if the soul of Ben Webster has finally flown from the man to be replaced by the menacing ersatz innocence of those Angelo Badalamenti soundtracks so many writers have (perhaps lazily) repeatedly likened the group's sound to. Musically, Bohren & der Club of Gore certainly continue their aesthetic shift towards the luminescent as proceedings enter daylight. The track titles themselves paint a picture less akin to the funereal than their forebears. 'Bei Rosarotem Licht' ('In Rosy Light') and 'Segeln ohne Wind' ('Sailing without Wind') litter Piano Nights' playlist, while 'Welk' ('Withered') or 'Skeletal Remains' is where these guys were at only two or three albums ago. But tonally the group are at their most coldly robotic on Piano Nights.

Fittingly, the piano sound across the record is not in fact that of an acoustic grand piano, but rather that of a Yamaha digital - a near-imperceptible mechanic simulation of the organic. Despite clambering out of the dank cave they were born in, the group shall never be unscathed; it's telling that their most 'upbeat' recording to date is also sonically their coldest and thinnest. Even the most distant whisper of 'happy' doesn't feel as comfortable for Bohren & Der Club Of Gore, but resultantly Piano Nights is in places their most emotionally-charged listen. 'Bei Rosarotem Licht' hangs by a gnat's wing throughout its duration, as the gradual pace and extended gaps between notes make their constant major key resolution all the more surprising. By evaporating the warmth of the Fender Rhodes - menacing as its outlook may have been - in favour of the digital piano, we're left with even more negative space than the group have previously allowed themselves. It builds further tension within those lumbering melodies, the unexpected major lifts constantly surprising around every corner, never reaching a full cadence.

The closing 'Komm Zurück Zu Mir' ('Come Back to Me') actually sees the re-appearance of guitar, this time a baritone guitar provided by Morten Gass, and their first use of a guitar in studio since 1995's Midnight Radio. Gass unleashes slight scatterings of tremolo-effect chords, allowing each note to rain down upon his bandmates with a comforting earthy normality amidst its synthetic surroundings. Bringing the guitar out of two decades' retirement in the last five minutes of an album that becomes, if not insists upon deep listening, is a pretty shocking move from a band that have never gone for shock when whispers will do. Symbolically, it implies something of a grand finale for the band; book-ending their catalogue with the same guitar notes that populated Gore Motel twenty years ago now.

With music of this unfamiliar, vaporous and instrumental sort, it's almost unavoidable that we construe our own inner narrative. To me, Piano Nights sounds like a demon's failed attempt at redemption, or the sound of some deep sea monster rising to the surface only to find itself instantly blinded by sunlight, or indeed a robot's weak simulation of inimitable emotions. There's a scene in James Whales' original 1931 film adaptation of Frankenstein where the monster, besotted with the simple joy of an innocent young girl throwing flowers on water only to see they float, picks up a child and playfully throws her in the water under the misguided logic that she will also float. The child drowns, and the monster cries, helplessly unable to shake the darkness that, besides wishing to overcome, irrevocably inhabits his very being. The demonic being that is Bohren & Der Club Of Gore capture that monstrous failure to appear human. Swapping in the piano seems like the move of a creature of good rather than the bacchanal evil of the Fender Rhodes - and yet they can't shake the darkness that is so intrinsic to them.

How much of this is theatre and how much truth has never been clear with Bohren & Der Club Of Gore, and the choice of digital piano over acoustic perhaps attests as much, preventing the shapeshifting sombreness of the music from becoming schmaltz, and keeping proceedings firmly in midnight movie land. With a sound as uniquely original as Bohren's, the most microscopic change can seemingly redefine everything, and those tiny shifts on Piano Nights do quite as much. The menace and late-night melancholy is subbed for outright tragedy and romance here, and this is certainly their best realised set released in the decade since Black Earth's high watermark, bringing together all that makes this music both beautiful and ugly, while tentatively exploring new sonic territory. It would indeed make a fittingly understated conclusion for the group, but here's hoping it's not. Besides, when you're going through hell, you should most definitely keep going.