Trombonist Shannon Gunn. (Astrid Riecken/for The Washington Post)

Jazz, the critic Whitney Balliett famously said, is “the sound of surprise.” Some are more surprising than others — like when the emcee at Blues Alley announces “Shannon Gunn’s Firebird Trio,” and the set turns out to mainly feature a quintet with piano.

Actually, nobody at the Georgetown club on Monday night should have been surprised. Chris Barrick’s vibraphone was set up onstage for all to see, as was Mikel Combs’s upright bass. Hope Udobi’s electronic keyboard stood adjacent to the house Yamaha grand, ready for him to hop onto its bench after three songs with the organ trio (more on that in a bit). Moreover, if anyone was surprised, nobody complained. The quintet did stellar work.

The texture alone gave them a unique launchpad, the vibes and piano blending remarkably well with Gunn’s trombone. She pulls her instrument away from its usual dark tones, emphasizing the fullness of its range and its ease of motion across that range, which brought it into rapprochement with the gauzy environs Barrick and Udobi created on “What It Takes.” That same fullness and versatility also reinforced them in the precarious clutter of “Orange Noise” — and its clatter, with the trombone often acting as a second drum to Norris’s rock-ish drive. The drummer also got off an effective, suitably noisy solo.

The quintet also allowed Gunn to show off her writing imagination. The highlight of the set was the premiere of a new arrangement for the 19th-century Anglican hymn “For the Beauty of the Earth” — “as you’ve never heard it before,” she correctly promised. Traditionally placid and unadorned, Gunn’s rendition sounded like a Carla Bley tune with its rhythmic motifs and overlapping colors.

The real surprise of the evening, however, came at the set’s beginning, when the Firebird Organ Trio played with no organ.

Udobi set his keyboard to play as a Fender Rhodes electric piano during the first three tunes. The difference was unexpectedly subtle, with the Rhodes sharing the organ’s long tones and luminous veneer. Udobi also played it with organ tendencies, with bebop language harking back to icons such as Jimmy Smith, a mix of both Horace Silver and James Brown-style funks on “Ms. Cheverly” and even some sustained pedal-point on the opening “Caravan.” Still, there’s a certain body, a gut-length presence especially in the bass register, that no organ substitute can provide, even with prowess like Udobi’s. Inspired and enjoyable as the set was, that element was missed.