Company, in Concert, presented by PCPA Theaterfest.

The 1970s references in this production began before a word was uttered, not only with the period-perfect costumes, but with such details as the vintage answering machine that Robert (Colum Parke Morgan) listens to when he first appears on stage. Among the messages he hears is one that gives away the premise of the evening, which is that we are at his surprise 35th birthday party. “Bobby,” as he is known, is the last single man among his circle of New York friends. The show’s two acts unfold in the time it takes for Bobby to blow out the candles on his birthday cake, as the various aspects of his complex relationships with five couples and the three women he is dating are played out in scenes, songs, and some hilarious dance numbers. If it sounds complicated, it’s not-the show won a score of awards in 1971 and has been in production virtually ever since. Company is considered one of Stephen Sondheim’s greatest works, and is frequently cited as a turning point in the history of American musical theater.

Valerie Rachelle’s direction is sharp and sophisticated, with lots of interplay between the actors and the onstage orchestra. From the great karate sequence with Sarah and Harry early in Act 1 to the sensational “Side by Side” dance sequence, which borrows moves from the classic showstopper repertoire, including the chorus line kick, the musical makes visceral the alternating glories and perils of being a single figure adrift in an ocean of singing and dancing couples. Morgan keeps his footing throughout, and delivers the lead’s big numbers with clarity, focus, and passion.

Sondheim managed to load this relatively small craft with a tremendous cargo of ambivalence. Stripped to its bare essentials, Company turns itself inside out and becomes a tool for investigating love, marriage, and the paradoxes of desire. Bobby’s singleness sets him up for a stream of ironic revelations, from the fact that one of his girlfriends is marrying someone else to a couple of different but equally unnerving come-ons from married or recently divorced friends. But the play’s dark vision of married life doesn’t let the couples get away smugly. There’s enough confusion and anger in their marriages to make this benighted single man their collective alter-ego. And from there, around it goes again in this classic take on the bittersweet sensation of blowing out birthday candles.