It's in the opening moments of "I Hear You," the first track on Inevitable Western: the mercurial, mysterious, yet utterly musical sense of adventure that lies at the heart of the Bad Plus' sound.

After recording the rigorous, mathematically challenging score for Igor Stravinsky's The Rite of Spring -- released only six months prior to this -- one can almost hear relief in the trio's return to its own universe.

These nine tracks are equally divided compositionally among bassist Reid Anderson, pianist Ethan Iverson, and drummer Dave King.

The bassist's aforementioned opener is a seemingly simple lyric stated by the piano but given a slightly quirky yet nearly processional tilt in its meter as Anderson illustrates the time as the drummer's syncopated accents add drama and humor.

King's "God Prisms Incorporated" is a marvelous cut-time jazz illustration of post-rock song form.

Iverson's pulsing chord statement rides atop the minimal melody, offset by the rhythm section's inventive interplay.

A piano solo commences halfway through, stretching the notion of time, though the tune never quite abandons its interlocking grooves.

Iverson's "Self Serve" is a knotty, almost swinging post-bop tune, with gorgeous harmonic statements by Anderson.

The mutant classicism in the bassist's "You Will Lose All Fear" feels like it was simultaneously influenced by both Charles Ives and Aaron Copland.

Iverson's solo, full of bright arpeggios and forceful dynamic chords, is adorned by King's hyperactive rolls and fills.

The set's longest piece is the drummer's "Adopted Highway." Introduced by a shimmering crash cymbal and a single piano chord, all three members engage in measured, dissonant stop-and-start counterpoint.

Iverson rumbles along the lower and middle registers as Anderson's pizzicato lines exhort King to use his brushes aggressively in response.

The tune unfolds very gradually, as free-flowing improvisation alternates with intricately written lines, building to a taut climax before gradually whispering to a close.

Iverson's "Mr.

Now" is almost funky in its intro.

His sharp, labyrinthine head is offered in short statements with King playing double time and Anderson holding the center.

It becomes a meaty, hard-driving exercise in modern post-bop, as all three members engage in spirited dialogue.

King delivers a bracing solo in the final third.

The closing title number, by the pianist, seamlessly melds jazz, classical, blues, modal, and great American saloon-style music in dexterous and lyrical phrases and rhythmic frames.

Inevitable Western is a reminder that the Bad Plus are not a "piano trio" in any ordinary sense of the term, but a unit of strikingly different voices acting as one in expanding the boundaries of jazz.