Mastodon set the bar high with Emperor of Sand.

It was written in difficult circumstances emotionally and creatively.

Like their first three albums (and unlike their last two), this is a concept album.

Its dominant theme is of time running out, and its 11 tracks offer an allegorical story of a man handed a death sentence by a desert sultan.

To escape, he flees into the expanse of the geography's emptiness, but the further he goes, the more lost he becomes in the sand as an unrelenting sun begins to claim his energy and ultimately his body -- think radiation poisoning.

Desperate, he attempts to communicate telepathically with tribes of various races and historical periods to make rain fall and stop that progression.

The concept is poignant: guitarist Bill Kelliher's mother passed away from brain cancer in 2016.

The music grew out of long jams intended to address his grief and help him heal.

The notion of time's eternal passage haunts every song here.

The return to concept is accompanied by the re-enlistment of producer Brendan O'Brien (he helmed Crack the Skye).

In an interview, bassist/vocalist Troy Sanders added weight to the expectations for the album: "...17 years in the making…it ties into our entire discography." Unlike their other conceptual endeavors (i.e.

Leviathan) Emperor of Sand's narrative is relatively simple.

While the conceptual framework harkens back to the early trilogy, the songwriting on this date is more reflective of the integrative styles on The Hunter and Once More ‘Round the Sun.

"Sultan's Curse," "Roots Remain," and the anthemic "Clandestiny" all roar with the bone-quaking riffery and roiling drum grooves, offering dynamic harmonic breakdowns, great solo spots, and plenty of fire.

Elsewhere, such as on "Show Yourself," "Ancient Kingdom" (both suggesting the influence of late-era Hüsker Dü), and "Andromeda," the focus shifts to hooks and melody first; the punishing riffs and monstrous drum fills are there, but are subservient.

The guitar interplay between Brett Hinds and Kelliher is, as usual, flawless, and the spastic drum and basswork of the rhythm section remains some of the most expansive in metal.

It's almost predictable, but it's not boring, and Mastodon's body of work has led listeners to expect it.

The eight-minute closer "Jaguar God" develops slowly and methodically from a lament to a dirge to a raging prog metal storm, offering a panoramic example of everything that makes Mastodon special.

Emperor of Sand is not perfect; it doesn't attain the glories of the first trilogy.

That said, it's easily on par with The Hunter and stronger than Once More 'Round the Sun, while being more diverse than any record they've cut.

Arguments about quality should go beyond the aesthetics to embody process and honesty, which are what ultimately matters.

In order to be true to themselves, Mastodon had to make Emperor of Sand at this time.

There was no other option.

As such, its urgency, sophistication, and emotional heft make it a necessary entry in their catalog.