For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Going about the events of her day, Clarissa reflects on the quality of her life in London and her marriage to Richard Dalloway. Her old suitor shows up unannounced and stirs up more feelings of the past, including memories of her erotic encounter with Sally Seton and of first meeting Richard. Meanwhile, Septimus and Lucrezia sit in the park. Lucrezia tries to remain calm as her husband demonstrates the disturbing signs of post-traumatic stress disorder.
Act II
Septimus is unable to face the possibility of living in one of Sir William Bradshaw’s psychiatric homes, so he commits suicide.
Act III
Clarissa’s party is underway and we learn that Sir William Bradshaw was once her doctor, too. She found him repulsive and thus feels deep empathy for Septimus, though she never knew him. The story ends with Clarissa feeling uplifted by Septimus’ great sacrifice, which she feels was made, in a sense, so she could once again see the beauty of life.