An autoclave.

It’s a pressurized device designed to heat liquids beyond their boiling points.

In the albumHeretic Pride, which is at least the fifteenth release from Durham’s hyper-prolific band The Mountain Goats, singer John Darnielle refers to his heart as just that. This is just one instance of the often strange, sometimes amusing, and always engaging images and characters that populate The Mountain Goats’ new record.

Darnielle has been The Mountain Goats’ primary and sometimes solitary member since the band’s 1991 inception. Since that time, The Mountain Goats have moved from the use of cheap tape recorders to actual studios, but have maintained an emphasis on lo-fi recordings and sparse instrumentation to accompany Darnielle’s signature nasal voice and highly literate lyrics.

Heretic Pride is often darker and more violent in its imagery than previous Mountain Goats releases, but its high points, as evidenced on songs like “Sax Rohmer #1” and the title track, are transcendent. Darnielle’s narrative-inclined lyrics are peppered with references to Norwegian death metal band Aura Noir, horror writer H.P. Lovecraft, former Oakland Raiders running back Marcus Allen, and the TV show Cheers to name a few. The music continues the band’s trend toward higher production values, which serve Darnielle’s songs well in most cases.

The album’s opener, “Sax Rohmer #1,” is a rhythmically tight, triumphant acoustic romp in which Darnielle’s shrill voice declares “With my own blood in my mouth / I am coming home to you / If it’s the last thing that I do.”

In “San Bernardino,” Darnielle delivers a hushed vocal over bouncy guitars, slow, steady string swells and what sounds like the sound of a spinning CD-drive.

“Heretic Pride” is by turns soothing and uplifting — until you realize the lyrics are the last thoughts of a man being killed by a mob — then it gets kind of uplifting again as he sings the defiant chorus, “And I feel so proud to be alive, / And I feel so proud when the reckoning arrives.”

The album sags a bit in the middle with “New Zion,” a generic slice of lazy-Sunday-afternoon musings about cults awash in organ, and “So Desperate,” a subdued acoustic ballad in which Darnielle’s voice is strained a little too much for some tastes.

Things pick back up, however, with “Craters on the Moon,” which starts with ominous string swells and slowly builds to the album’s sonic climax as cellos or violas weave around crashing acoustic guitar and snare drum. The song shows the force Darnielle and company can muster with lean instrumentation.

With Heretic Pride, The Mountain Goats maintain the musical integrity and originality they are known for after their nearly two-decade career, an impressive feat in the often capricious indie scene. If this album is any indication of the future, The Mountain Goats should be sending us gleefully to Wikipedia on quests to decipher their lyrics for a long time to come.