Lights rise on Clara astride Giorgio, as they make love passionately. She falls into Giorgio's arms and looks into his eyes. The two are entirely consumed by their love for one another ("Happiness – Part I"). The mood darkens when Giorgio, who is a soldier, informs Clara that he has received his orders from headquarters; he is leaving Milan for a remote military outpost in five days. He tells her that even though he will be far away, they'll still have each other. They agree that each never knew what love was until they met the other; Clara pleads with him not to go ("Happiness – Part II").

We go to an Officers' Mess Hall at the outpost. Colonel Ricci, Lieutenant Torasso, Major Rizzolli, Lieutenant Barri and Doctor Tambourri sit around a table for dinner. The cook, Sergeant Torasso Lombardi, is overseeing the proceedings. The men are suddenly interrupted by a woman's scream, which they momentarily acknowledge before resuming their conversation. Giorgio enters, and everyone rises to greet and welcome him. The talk turns to Giorgio, as the men praise him for all his military triumphs.



The scene then splits between Clara, who reads a letter from Giorgio, and the men at dinner. In the letter, Giorgio tells Clara that he cried the entire train ride when he left her ("First Letter"). At the table, the men hear music coming from upstairs. The Doctor tells Giorgio that the Colonel's cousin, Signora Fosca, is playing the music. She is in such poor health that it is a continual worry; she stays in her room most of the time. Her only real passion is reading, but she's read through all of the books that the Colonel can find. Giorgio also loves to read and he is happy to lend Fosca some of the books that he has brought. Private Augenti enters and delivers a letter to Giorgio from Clara. She, too, has been crying because she misses him ("Second Letter").



The scene resumes as another scream is heard from upstairs. The Colonel assures Giorgio that it is only Fosca. The Doctor rather routinely rises from his chair and goes up the stairs, even though he makes it very clear that there is absolutely nothing to be done. The Colonel reassures Giorgio that he will get used to the life amongst them.


Next, Giorgio oversees a formation of soldiers performing their marching exercises. He writes to Clara and tells her how much he hates the sterile little town, the pompous little men and the military madness ("Third Letter"). He still thinks only of Clara and begs her not to forget him. The Doctor enters and observes that the soldiers appear to be responding well to Giorgio's command. He wants to be certain that things are going well for Giorgio and that Fosca's occasional outbursts have not unsettled him too greatly. Giorgio questions the Doctor, wanting to know exactly what is wrong with Fosca – she has a collection of many ills, a kind of medical phenomenon. Oddly enough, she isn't in danger of succumbing to this disease, since her body is so weak that it doesn't have the strength to produce a mortal disease. Giorgio wonders if she's the Colonel's lover, but the Doctor tells him that her physical state prevents her from being anyone's lover.

We segue back to the hall. It is morning. Rizzolli and Barri are finishing their breakfast as Giorgio joins them. The cook clears Fosca's place; once again, she has not shown up for a meal. Hearing the bugle call, the others leave Giorgio alone to eat his breakfast. Giorgio takes out a letter from Clara. Naturally, she misses him. Every time she walks through the park, she sees the bench where they first met. She imagines them together in the little room where they shared so many happy times... and where they will be happy again ("Fourth Letter").



Fosca suddenly enters the room with some books and approaches her empty place setting. We discover that she is an ugly, sickly woman. Giorgio is momentarily stunned. She greets him nervously and thanks him for his books – reading is the only comfort that she has. There, she can live in her dreams, as opposed to the horrible realities of her life ("Fosca's Entrance – Part I"). She invites Giorgio to join her on a day when she is feeling better, so that she can show him the gardens and the nearby ruined castle (Fosca's Entrance – Part II"). He accepts the invitation.

She gets up suddenly and leaves the room. We hear the distant sound of funeral drums. Fosca returns, carrying a small bunch of flowers, which she offers to Giorgio. She is surprised that he hasn't noticed their greenhouse. As they look out at it, they hear and see a hearse drawing up to the greenhouse, looking for flowers to adorn the casket. Suddenly, Fosca begins to tremble, lets out a terrible cry and collapses to the floor. Giorgio cries out for the Doctor, who enters with attendants that carry her off. Giorgio just stands there, revealing the contents of his letter to Clara and describing the wretched scene that he has just witnessed ("Scene 3 – Part I").



The Colonel, the Doctor and Fosca enter and stroll through the garden down to Giorgio. The Colonel and Doctor talk alone while Fosca and Giorgio stroll a bit on their own. Once again, Fosca bemoans her sorry situation. Giorgio tells her that there must be hope for her getting better; Fosca assures him that there is not. Giorgio tells her to concentrate on everything around her that suggests beauty, life and a special kind of love; true love that exists between two people ("Scene III – Part 2"). Fosca accuses him of cruelty; she confesses to Giorgio that she has watched him from her window since the first day that he arrived. She knows that he is different from the rest and asks him to be her friend ("Scene 3 – Part III"). He tells her that she will, of course, have his friendship. The Colonel and Doctor take Fosca back, since she is burning up with fever.



Clara and Giorgio correspond once again. Giorgio has told Clara that he is worried that he has opened a door with Fosca that would have been better left closed. She assures him that there was nothing he could do but to be her friend. After all, her cousin is his direct superior, and he needs to think about his career. However, he needs to keep his distance and make certain that she doesn't misunderstand his intentions.



Three days go by, and Giorgio does not contact Fosca; rather, he avoids her. Fosca slips a letter under his napkin that states how upset she is that he hasn't visited with her. Although he may disappear, she will not. Giorgio comes to dinner, and Fosca is there, at the table. She insists that Giorgio read the letter. He lashes out at her; it is obvious that she is obsessed with him. He asks the Colonel if he may take a leave of at least five days; it appears that he is needed in Milan on an important matter. Although annoyed, the Colonel grants Giorgio his request. The other soldiers sing lines from Clara and Giorgio's letters ("Transition Scene 4-5").



The next morning, Fosca stops Giorgio on his way to the train. She begs him to think of her while he is gone. He politely dismisses her. She throws herself at his feet, asking if he can at least love her the way that he would love a dog. He pulls her up and calms her down by promising to write her while he is gone. Giorgio goes to see Clara and writes Fosca, as promised. His letter contains information that Fosca would rather not know; he tells her that he is in love with someone else. He asks that when he returns to camp, they begin anew, acting as though they have never met ("Fifth Letter").

Upon his return, Giorgio visits Fosca, who is sicker than ever. She asks about his love for Clara. He tells her that Clara is a married woman whom he adores. Learning all of the details of the relationship, Fosca asks that Giorgio never come to visit her again.



Three weeks pass, and Giorgio doesn't see Fosca. He writes Clara that things have greatly improved, al though in reality, the little town and all of the military maneuvers are driving him a bit crazy ("Three Weeks"). The Doctor calls for Giorgio to tell him that Fosca has taken a turn for the worse and is mortally ill. She is letting herself die for Giorgio. The Doctor says that the only thing that can save her life is for her to see Giorgio.


Giorgio goes to visit with Fosca, who lies sick in bed. She asks him to write her a letter, which she dictates to him. In the letter, at her insistence, he tells her that he loves her ("Scene 7 – Part II"). He gives the letter to her and obliges her with a requested kiss. She pulls him towards her passionately. Giorgio pulls himself away and runs from the room. After a moment of calm, Fosca screams.



The next morning, the soldiers comment on how Fosca's screams are driving them all crazy ("Scene 8"). The Doctor thanks Giorgio for going to see Fosca, although Giorgio questions the validity of his request. Later on, the Colonel thanks Giorgio for visiting Fosca. He tells Giorgio that his parents died when he was very young, and that Fosca's mother and father welcomed him into their house whenever he was on leave. Fosca was a happy girl, although not the most beautiful. The Colonel confesses to introducing Fosca to the handsome Count Ludovic of Austria, who charmed her and ultimately asked for her hand in marriage ("Flashback – Part I"). Once the Count got Fosca's hand and received her sizable dowry, he gambled away her money and cheated on her ("Flashback – Part II"). When confronted, the Count abandoned her ("Flashback – Part III"). Fosca then returned home to find her parents impoverished and in poor health. Her own health began to fail, and she began suffering the first of her convulsions. She went and searched for her husband; he was nowhere to be found. Her parents both died, and she came to live with the Colonel, who in some way felt responsible for the circumstances ("Flashback – Part IV").



Clara writes Giorgio another letter; this one is a bit more melancholy. She is worried that the next time they see each other, they will be old and gray ("Sunrise Letter"). As Giorgio reads the letter, Fosca creeps up on him and asks why he has been avoiding her since her recovery. Once again, she is acting possessive and slightly manic. She begs him for a kiss, but he recoils. She then grabs his hand and kisses it herself. Giorgio finally loses his patience and tells Fosca to leave him alone. What she finds to be love is more like a curse to him ("Scene 9"). Rain and thunder begin, and Fosca goes to leave. On her way out, she falls. Initially, Giorgio walks past her, but he returns to carry back to her room.



Back in the barracks, the soldiers question Fosca and Giorgio's relationship. They know that the only reason that she comes to every meal is because of him. Several of them also bet that Giorgio will be promoted to General by next week ("Scene 10").

Time passes, and Giorgio has nightmares of Fosca dragging him down into the grave with her ("Nightmare"). The Doctor comes in to calm him and explains that Giorgio became ill after carrying Fosca back in the rain two days ago. The Doctor puts Giorgio on a forty-day sick leave in Milan, hoping that this will end the relationship between Giorgio and Fosca.

Giorgio gets well enough to take a train to Milan. Clara is ecstatic at the news ("Forty Days"). However, Fosca has followed Giorgio onto the train. She promises to stay out of his way. Again, Giorgio asks her to leave him alone and face the facts. She tells him that it isn't a choice that she has made – she loves him and has no control over it ("Loving You"). Before this can go any further, Giorgio gets off the train at the next stop so that he can escort her back home.



Back at the camp, Giorgio talks with the Doctor, who apologizes for having brought Fosca into his life. The Doctor, being one of Giorgio's superiors, even offers to help get Giorgio transferred for good. Strangely enough, Giorgio refuses this. He feels as if it is his duty to help Fosca. The Doctor tells him that this is ridiculous because no one can help her. The soldiers speculate that Giorgio is on leave because he is in too deep with Fosca ("Scene 11").

In Milan, Clara and Giorgio meet, and Clara gives Giorgio what she thinks is the greatest news of all. Her husband is going to Rome for a few days; they'll be able to spend some wonderful nights together, not simply their shuttered afternoons ("Scene 12"). Giorgio tells her that he isn't going to take the forty days of sick leave. Instead, he will only spend four days with her in Milan. Clara is infuriated by this and accuses him of being obsessed with Fosca. He tells her that he has a responsibility to her. He presses Clara to leave her husband and live with him. She reminds him that she would lose her child if she did. Giorgio begs her to take the child and run off with him. She can't leave her present obligations. They declare their love for one another and decide to enjoy the next four days together.



Giorgio returns to the barracks in time for the annual Christmas party ("Christmas Music"). He is met with some rather startling news from the Colonel: Giorgio has been transferred back to headquarters immediately. Upon hearing this, Fosca throws herself into Giorgio's arms and begs him not to leave. Seeing this, the Colonel reprimands his cousin like an errant child, and she runs off screaming. The Doctor follows right behind her.



Clara writes Giorgio, begging him not to let things change things between them. Maybe she'll leave her husband when her son goes off to school, but until that time, there is nothing that she can do ("Scene 13"). Giorgio realizes that the two of them see love in a very different way. The Colonel enters angrily; he has the letter that Giorgio wrote to Fosca – the one that she dictated to him. The Colonel feels betrayed by Giorgio. Their argument becomes so heated that the Colonel challenges Giorgio to a duel. The Doctor tries to intervene and asks Giorgio to explain what really happened; however, Giorgio stands silent. The Colonel asks that Fosca hear nothing of this matter, and Giorgio obliges his request.


Giorgio goes to see Fosca, against the Doctor's orders. He explains that he had nothing to do with the transfer. She knows that now, because the Doctor told her. Giorgio tells her that his affair with Clara is over. He thought that he loved her but he realizes that no one has loved him as deeply as Fosca. Love without any judgment is what Fosca has given him, and he cherishes it greatly ("Scene 14"). Before he leaves her, she pulls him towards the bed. They kiss as he carries her to the bed. He starts to leave, and she pulls him down onto the bed.



The next morning, Giorgio and the Colonel have their duel with pistols. The Colonel falls to the ground. Giorgio, standing alone, lets out a high-pitched howl – much like Fosca's.



Some time later, Giorgio sits in a daze at a desk. A nurse enters and brings him a letter from the Doctor. Fosca died three days after the night that Giorgio last saw her. She knew nothing of what took place between him and the Colonel. The Colonel's wound was serious, but not mortal. He recovered in a few months. The Doctor confesses that he never tried to convince the Colonel of Giorgio's innocence, fearing that it might do more harm than good. He sent a box with papers that Giorgio had left behind in his desk. The Doctor also enclosed some personal belongings of Fosca's and a letter that she had written to him just prior to her death. Her letter, although stating that – for once – she wanted to live, says that she was able to die in peace, knowing that true love was hers at last. Giorgio sits alone with the letter and his memory of Fosca ("Finale").