With no violence, no bare breasts, no sex scenes, no on-screen chest waxing, and few profanities stronger than “Shoot,” Michael Showalter’s “The Baxter” glides into place as the third near-perfect romantic comedy of the summer. Like “Wedding Crashers” and “Must Love Dogs,” Mr. Showalter’s movie doesn’t break the ironclad rules of the genre. Rather, it embraces them with a near-religious zeal. The final result is a mild-mannered, charming labor of love.

“The Baxter” concerns a “Baxter,” defined as the third wheel in a romantic comedy. He’s the other guy, the one who isn’t right for the leading lady but who comes awfully close to marrying her before she’s rescued at the last minute by her true love. The Baxter is the guy who doesn’t understand passion, the stable, unromantic fellow the heroine is willing to settle for while she waits for her true love to come to his senses and rush to the chapel and save her from a bland life.

Here, the titular Baxter is Elliot Sherman (Mr. Showalter), a chartered accountant who has a hat for every occasion and whose favorite color seems to be tweed. Elliot is ditched at the altar by the love of his life, Caroline Swann (Elizabeth Banks, who was one of the few highlights in “The 40-Year-Old Virgin”), when her true love, scientist Bradley Lake (Justin Theroux), races back from a geode-mining expedition in Malta to confess his deep, unshakable feelings for her.

The rest of the movie is a discursive, occasionally rambling, flashback showing how things reached this point. It’s a romantic comedy told “Rosencrantz and Guildenstern Are Dead”-style, from the point of the view of a minor character.

But Sherman is not just an innocent victim of romantic comedy conventions, he’s also a perpetrator – he’s got a Baxter of his own: Cecil Mills (Michelle Williams). Fresh off the bus from Minnesota, Mills is a temp worker filling in for Sherman’s secretary; a connection blooms when they both disclose that they read the dictionary for pleasure.

As Swann calls her wedding to Sherman off, then announces that it’s back on, then insists on flirting with Bradley, Sherman is sent spiraling into black depressions. Fortunately, the sparrow voiced Mills is there to offer solace. Unfortunately, every time Mills is about to open her heart to Sherman, he stomps on it by running back into the fickle arms of Swann.

This is a fairy tale set in a storybook New York, meticulously crafted in every detail. Everyone in “The Baxter” speaks in complete sentences and with a supernatural precision that precludes contractions. From its woodsy restaurants and bars to its cramped apartments, impenetrable party games, miniature wedding planners (played by Peter Dinklage, who should do more comedy), and strict hierarchy of who drinks what at a bar, this is a movie made by people who obviously like to think about things far too much.

It’s also a movie about WASPs, their fussy table settings, their blah chic clothes, their ridiculous pronunciation of exotic locales, and their withered sense of humor. This movie does for the frozen Anglo-Saxon souls of the Northeast what “Annie Hall” did for Jews: It pulls their every neurosis into daylight, so we can all laugh at them.

The laughs in “The Baxter” aren’t nonstop, but when they do come they’re surprising, original, and never cheap. This being a romantic comedy, there’s a final chase (this one on foot from Brooklyn to Washington Heights, via Chinatown), a confession of feelings, and a happy ending. But stick around for the credits, where a final footnote discloses the eternal injustice of being a Baxter: Wherever there are two lovers, there’s always a guy who didn’t get the girl. Mr. Showalter’s message: Love hurts, but it doesn’t have to be rude about it.