If I were to sum up my experience of watching “Seen Change!” in a word, it would have to be celebration. The musical at once celebrates the history of New Haven and the Shubert Theater, and the spaces and figures we tend to overlook — the backstage and people behind the scenes.

The show is a production of the New Haven-based A Broken Umbrella Theatre, which specializes in site-specific performances that draw on local histories. In keeping with this tradition, “Seen Change!” — their newest musical — opens in the lobby of the Shubert Theater. After about five or 10 minutes of theatrical chaos and frantic action, the performers take the audience to the Taft Hotel next door for Act II of the play.

“Seen Change!” tells the story of an out-of-town theater ensemble performing an adaptation of a fictitious musical, “Your Heart is in My Hands.” The adaptation, made in 2015 with an entirely new cast, production and lyrical team, hopes to restore the unfinished musical to its rightful place by finishing Willoughby’s finale. But when a theater apprentice breaks the “ghost light” — a charm against bad luck — things go haywire, and ghosts from the past version of the musical suddenly appear.

As the past and present composers unite after much conflict to put together a finale for the play, “Seen Change!” captures the action and chaos that takes place before any performance. The theater apprentice Lisa, the lyricists Willoughby and Dana Wasserman, and the stage manager Jane, all backstage people rather than actors, take center stage. An energetic tap dance routine by Dana Astmann and Aric Isaacs, perhaps my favorite part of the performance, highlights the role of theater technicians: to ensure that the actors “are not dancing in the dark.” Mary Jane Smith and Michael Peter Smith , the present and past producers of the show, are wealthy and domineering.

“Seen Change!” innovatively uses all parts of the rooms the actors perform in, as well as the multiple levels of the Shubert Theater, where they return for the third act. They converse now and then with the audience, which is supposed to play the role of the play-within-the-play’s sponsors, with the actors mostly apologizing and confidently reassuring the audience that “everything is absolutely fine.” The first two acts were slightly chaotic and lengthy. Characters emerge from different directions and shout out fast, sometimes incomprehensible dialogue, and the audience is left standing (which I found to be a little uncomfortable). “Seen Change!” nevertheless promises to keep the audience actively engaged throughout.

Through its interactions between characters from different eras, “Seen Change!” makes for a meta-theatrical musical comedy. The competition between Willoughby and Wasserman as they struggle to put together a finale allows for some occasional laughs. The play also effectively explores the drastic changes in culture and etiquette across time. The proud Willoughby is highly offended when he is told that he cannot smoke in his own theater, or, as a matter of fact, outside it. One of the characters from the past sneers at the audience in the Taft lobby: “They went to a night at the theatre dressed like that?” A series of cross-era “show-mances” also adds humor and entertainment.

Despite these differences, some things never change with time, and nothing exemplifies this more than the theater. Each of the characters yearns for a second chance, whether it’s Willoughby, who wishes that he could have written his finale to the musical, or Lisa, who wishes she had not broken the ghost light. Ultimately, though, very little is in their hands. As the producers aptly put it in their musical duet, “Nothing is certain except the curtain will go up.”