Old Lyme — These final Musical Masterworks concerts in May are always bittersweet. The lilacs bloom outside the First Congregational Church and the daylight lingers through early evening's closing notes to announce the season's change. The last programs tend to be seductive, whispering — at times shouting — come back next year.

Saturday's was no exception, as series Artistic Director Edward Arron staged a program, to be repeated at 3 p.m. Sunday, that looks like the musical equivalent of a European union. Concluding Masterworks' 21st season of chamber music here, we have a little German, a little Czech, some Russian and a lot of French.

The major work of the program was Fauré's Piano Quartet in C Minor, Op. 15, a most theatrical piece, in that its true pleasures of musical interplay are best seen as well as heard to fully appreciate the exchanges between musicians. But the program was salted with charming oddities and spiced with a riveting Prokofiev violin duo.

Featured in Prokofiev's 1932 Sonata in C Major for Two Violins, Op. 56, were Yehonatan Berick and Carmit Zori, with Zori taking over the four-concert tour for the scheduled Steven Copes, who is preoccupied as a new father. This sonata is a transitional work, partly the radical Prokofiev, the young "Man of Steel," and partly the composer to come, who sang to the masses.

Berick and Zori performed it to fine effect, standing side by side through its musical lilacs and thorns. The opening andante cantabile began with Zori taking the high, dramatic role and Berick the dark, soulful one and ended in a meltingly beautiful unison. The duo chased each other through an often fierce allegro before uniting in a slow movement in which they played sonic tricks, as the lyrical leading voice slid from violin to violin almost at random, like revealing the inner voices of a fugue. The finale, with Zori at times muting to create contrast, was powered by dance rhythms, and the duo sharing dissonant, grinding stops that seemed a full-body experience.

The program opened with one oddity: Schubert's Piano Trio in One Movement in B Flat, D. 28, with cellist Arron and pianist Rieko Aizawa joining Zori. This work by a 14-year-old Schubert and discovered in 1922, almost a century after it was written, has all of the rhythmic and melodic flair of his later works, without the enharmonic drama, and the Masterworks trio played it quick and high-key.

The other oddity rolled out a first in the series' two decades of concerts: a harmonium. Aizawa sat down – and we do mean down – at the little, foot-pumped organ for Dvořák's 1878 Bagatelles for Two Violins, Cello and Harmonium, a set of sweet, five easy pieces written for amateurs. As Arron noted, "Before there was television, there was chamber music."

Drawing on folk tunes and structures like the fast-slow dumky which we associate with Dvořák, the five bagatelles set the strings singing above the low, humming voice of the harmonium, which gave the Old Lyme audience something new … or should we say, old? … to tickle the ear. The harmonium on stage, a relic of a bygone era, was reinforced in places with duct tape.

Amid this musical simplicity was the oddest of minuets, full of dotted notes that gave it a stuttering effect to defy dancing, and in the final two movements, the natural decay of the harmonium running out of air tapered off the sound naturally to end it all.

After intermission, the four musicians gave a wonderfully rich and sonorous reading of the 1879 Fauré quartet, with Aizawa at the center of it all. This unusual piece, written while the Brahms vs. Wagner aesthetic wars were raging, sets the strings as something of a choir, a trio of voices singing to the piano. And as Berick, now on viola, Zori and Arron explored the thrilling acoustics and sonic richness offered them, Aizawa carried the piece forward again and again.

To experience this quartet in concert is largely to savor the motion, the fracturing of the string trio into separate voices then reuniting and the interplay between the trio and piano – and each other. But the work thrives on nuance, and Saturday's musicians performed that handing off of ideas and sharing of themes with a oneness and sure sense of line that brought out all of the drama and beauty of this classic.

The adagio should stick with all who experienced it. It was sonically thrilling, with the deep string voices of Berick and Arron rich and dark, and emotionally powerful, quavering in a twilight between yearning and resignation, between restlessness and repose.

This one movement alone reminds us why we go to Masterworks, and why May is bittersweet.

m.moore@theday.com