Act I

It is 1933, closing time at a restaurant in San Francisco. A group of tired waitresses bemoans the fact that "a waitress earns her pay" (Ooh, My Feet). Amy, another waitress, rejects the crude advances of the cashier. Cleo, her friend, and the other waitresses offer their sympathy (I Know How It Is). Amy discovers that a customer has left her an amethyst tie pin and a letter (The Letter). The letter, written in broken English, contains a proposal of marriage for her - or "Rosabella," as she is addressed in the letter – from Antonio Esposito, who lives on a grape ranch in the Napa Valley. She is touched and decides to answer the letter (Somebody Somewhere).

The scene shifts to the main street of Napa, three months later. Tony Esposito appears in a state of exhilaration. After carrying on a correspondence with his Rosabella, she has sent him a picture and asked for his in return (The Most Happy Fella). Tony's spinster sisters Marie and Therese try to spoil his plan to marry Rosabella, reminding him that he is neither young nor good-looking (The Letter theme). Herman, one of Tony's ranch hands, and his friends, Clem, Jake and Al pursue their favorite hobby: girl watching (Standing on the Corner). Joe, Tony's attractive young foreman, informs his boss that he'll soon be moving on (Joey, Joey, Joey). Tony has an idea: he asks Joe to have his picture taken on the spot, explaining that he wants it to remember him by. Tony decides to send Joe's picture instead of his (Rosabella).

A few weeks later, on Tony's farm, Tony's servants prepare a banquet for the wedding of Tony and Rosabella, scheduled for that evening (Abbondanza). Tony is getting ready to collect Rosabella from the station, but becomes upset when he learns that Joe has not yet departed. In a state of agitation, Tony drives off in his truck, as all the neighbours begin to arrive and the party swings into gear (Sposalizio). Rosabella appears, having been escorted by the postwoman (Special Delivery!). The servants and Joe welcome her (Benvenuta). Left alone with Joe, Rosabella expressed her satisfaction (Aren't You Glad?), but when she addresses Joe as Tony, she learns of the deception that has brought her to the ranch. She is about to leave when Tony, almost lifeless, is carried in. He had an accident with his truck. Realizing that she has no place to go, and over the objections of Tony's sisters, Rosabella agrees to marry Tony at once. After the ceremony, Joe tries to console Rosabella (Don't Cry). They are drawn to each other, unable to resist their feelings.

Act II

A week later, in Tony's vinyard, the workers are busy (Fresno Beauties). Tony, heavily bandaged and in a wheelchair, protests his state. The doctor suggests he turn to Rosabella (Love and Kindness). Left alone, Tony and Rosabella decide to start their relationship over, from the beginning (Happy to Make Your Acquaintance). To Rosabella's surprise, Cleo and two other waitresses appear. Tony has hired them so she won't be lonesome. Marie and Therese try to enlist the girls as confidantes, but without success (I Don't Like This Dame). Cleo meets Herman, and they soon discover that they have something in common (Big 'D').

Later in May, Rosabella's affection for Tony grows. Watching the workers dance, Tony's sisters declare that "old people gotta get left behind" (Young People). When Rosabella dances off with the young people, Tony decides that their words are true (Old People). Cleo is furious when she sees how the other hands take advantage of Herman's good nature, but Herman just can't help it (I Like Everybody).

It's June, and Tony is on his feet, learning to walk again. Rosabella decides to tell him what her feelings for him are (Like a Woman Loves a Man). Tony is overwhelmed. They declare their love for each other (My Heart is So Full of You). Tony decides to throw a big wedding party that evening. He invites everybody and the celebration commences, but when Rosabella is whirled in the dance, she faints. The doctor's diagnosis: she is pregnant!

The servants prepare the celebration (Abbondanza reprise). Meanwhile, Herman has been the victim of another practical joke. Cleo has had enough of it (Goodbye Darln'). The doctor asks the neighbors to give Tony and Rosabella a little time alone (Song of a Summer Night). Rosabella confesses to Tony that she is carrying Joe's baby. Tony is furious and orders her off his property. She leaves and Tony learns from Pasquale, his servant, that Joe is down at the station, preparing to leave town. Tony takes a pistol and goes off, determined to kill Joe.

At the depot, Tony learns that Joe has already left. Alone, he realises that Rosabella has no place to go (She's Gonna Come Home with Me) but before he can tell her, his sisters appear. They urge Tony to forget about Rosabella, Cleo appears and defies them. The desperate sisters snatch the cane from Tony's hand. Cleo lunges at them and they struggle. Pasquale tries to break up the fight. Herman, who enters during the melee, knocks Pasquale out. Cleo is overjoyed that Herman has finally stood up for himself and for her (I Made a Fist).

Tony asks Rosabella to come back, saying that he will tell everybody that the baby is his. He convinces her that they should start all over again and finally Tony learns Rosabella's real name. Tony and Rosabella are together and Tony is indeed the most happy fella in the whole Napa Valley (Finale).