THE BEMUSED affection with which Clifford remembers his jazz trumpeter father Gene has consumed many sons in many other dramas, yet Side Man, Warren Leight's Tony-award winning play now at ACT, succeeds in portraying the frequently heartbreaking way one man helped to shape his son's soul. Blessed with Narelle Sissons' set and Eric Chappelle's sound design surrounding the audience in memory, Mladen Kiselov's production is a rewarding, if imperfect, evening of theater.

Clifford (Drew Ebersole) guides us through time, narrating the rise and fall of not only his father's beloved music but of that more elusive tune that was once his family. "He could sense everything when he was blowing," Cliff says of Gene (John Procaccino), "and almost nothing when he wasn't." Director Kiselov does a wonderful job of staging the emotions that stem from that flaw. In one inventive bit, Gene finishes the last few bars of a performance, just visible through one of the space's exit doors, while future wife Terry (Marianne Owen) breathlessly watches from center stage and Clifford, omniscient, sits upstage watching her, almost overcome at the sight of both his mother's joy and her imminent defeat.

The production can be squeaky clean when the play is not, probably because Ebersole, as our link, needs some hidden edginess, and is sometimes in danger of morphing into Eugene Morris Jerome, the affable narrator of Neil Simon's Brighton Beach trilogy. He's very appealing, though, and we care for the people he wants us to love because of it. More potentially damaging is the weak, crucial performance of Procaccino, whose casualness misfires. When Procaccino holds back, he disappears, especially when he's in the company of Owen, whose rich, feisty performance is her best in years. There are also vibrant turns by Cynthia Lauren Tewes (a hoot as a much-married jazz groupie) and by most of Gene's buddies (Keith Scales as an ex-junkie is right on target).

Sometimes boisterous, sometimes melancholy, and sometimes, deftly, both these qualities at once, ACT's Side Man often resembles the vital music it celebrates.