Walk into Act II Playhouse in Ambler and you get a warning.

NOTICE FROM THE PLAYWRIGHT

, it says in bold, black letters on the inside cover of the playbill for the musical

I Sent a Letter to My Love

, whose book and lyrics are by Jeffrey Sweet, with music by singer-composer Melissa Man-chester.

Anything you are about to see on Act II's stage "may or may not be what we wrote or intended," cautions Sweet, the well-regarded playwright who teaches a course at the University of the Arts. It turns out that director Frank Anzalone, musical director Collin Maier, and the Act II production team cut or rewrote parts of the script and changed melody lines. In his note, Sweet asserts his artistic ownership and disowns Act II's new vision.

This begs the question: If Act II is rewriting people's plays, why didn't it start months ago with the insipid Scotland Road, which could have been overhauled entirely? Pity, such missed opportunities.

But, of course, the larger and serious question is this: Why put on a play if you don't want to put on the actual play?

The show Act II is presenting "doesn't feel like our work anymore," Sweet writes. Under an agreement that allows the theater to continue with the disputed production, Act II cannot market the play in some ways that professional theaters do.

Critics, for instance, are not invited. Which insured that I would go on my own to see I Sent a Letter to My Love, about a sister and her brother, a polio victim who moves by wheelchair, in the wilds of Maine. It's set in 1954. The period kitchen designed by John Hobbie and the '50s costumes (lots of plaid) by Alisa Sickora Kleckner are knockouts.

The plot is simple: Love-starved sis puts an ad in the local for a pen-pal, and she gets a reply from love-starved bro, pent-up with his disability. She decides to assume a persona, and the two keep exchanging letters. The deception lasts and lasts - then, bro demands a visit from his correspondent.

"The show Melissa and I wrote was intended to be darker and more operatic," Sweet says in his notice, and I can attest that it is neither in Act II's vision - the only version I've ever seen. It seems weightless.

It's performed by a good cast, for sure, but it's a two-hour dive into sop. People sing, "Let's take a chance and start to dance," and about birds flying and breathing the summer air, about two hands touching, and two lips touching, and two hearts touching. How touching!

The icky quality of the Act II show is complete with dialogue that changes emotion within a line or two, and who knows why? The accompanying orchestra sounds limp often, pleading for even a hint of percussion (and never getting it). The show is at its best when the siblings, nicely done by Therese Walden and Dan Schiff, recite or sing their letters to each other, and when the deception comes to a head.

Barbara McCulloh gives a good ride as the woman renting some of the sibs' property, and so does Michelle Horman as an amateur actress trying to further the deception; Horman's scenes are the snappiest in a thin musical that's too long.

Jon Reinhold has the unenviable job of playing the ghost of an old flame of the sister's; he's a constant memory and maybe an alter ego - a irritating device, popping up like ragweed.

If you fool with a script, folks, don't be shy: X-out a character altogether.

I Sent a Letter to My Love

Book and lyrics by Jeffrey Sweet, music by Melissa Manchester, directed by Frank Anzalone, musical direction by Collin Maier, set by John Hobbie, costumes by Alisa Sickora Kleckner, lighting by James Leitner. Presented by Act II Playhouse.

Cast: Therese Walden (Amy), Dan Schiff (Stan), Barbara McCulloh (Gwen), Michelle Horman (Miss Morgan), Jon Reinhold (Jimmy).

Playing at Act II Playhouse, 56 E. Butler Ave., Ambler, through June 10. Tickets: $25-$40. Information: 215-654-0200 or www.act2.org.

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Contact staff writer Howard Shapiro at 215-854-5727 or hshapiro@phillynews.com.