With the addition of saxophonist Wayne Shorter, Miles’ second great quintet was born. The trumpeter’s new sidemen began to contribute compositions on this album. Shorter’s mercurial title track uses melodic progressions that suggest a moving tonal center—a tricky structure that the band handle with ease. But not all the impressive moments are abstract: There’s a hint of finger-snapping soul jazz on “Eighty-One,” a tune coauthored by Davis and bassist Ron Carter.