Here’s an exercise for the blocked writer: Write what you don’t know about what you know. That’s the approach the unnamed narrator of Deirdre Madden’s ninth novel chooses. She takes her friend of 20 years and revisits memories from their times together, wondering whether she truly knows her. And in doing so, she conquers her writer’s block and creates this novel, Molly Fox’s Birthday.

Madden’s book, a finalist for the Orange Prize, is so honestly told that it feels less like fiction than personal revelation. The action takes place on a single day, June 21, the longest day of the year, which is also (of course) the birthday of an Irish woman named Molly Fox. Molly, as she always insists, is an actor, not an actress (“If I wrote poems would you call me a poetess?”), and the narrator is the playwright who jump-started both their careers with her very first play. While Molly is off performing in New York, the narrator has borrowed her friend’s cluttered home in Dublin, where she tries, with much difficulty, to begin a new play. The narrator used to believe that Molly hated to celebrate her birthday because she was insecure about her age. What the narrator later learned was that June 21 was the day Molly’s mother abandoned her family.

Any story about writers and actors is implicitly a story about characters: how and why they change; how one creates or becomes someone unlike oneself. The question the narrator ponders is whether Molly has ever changed. You might say that because Molly communicates her deepest self as an actor, she is always changing. But you might also say that her chameleon nature allows her to avoid acknowledging that deepest self. Just as the narrator identifies herself only as a writer, Molly identifies herself only as the characters she becomes on stage. “All I ever wanted was to be myself,” the narrator remembers Molly saying. “Who am I? Who am I? I never again heard that voice screaming in my head. I now knew exactly who I was. I was an actor.”

Molly’s artistic discipline provides her sense of self. It is what draws her to the narrator, but it is also what makes them more like acquaintances than intimates. Yet “I would not be the writer I am without Molly,” the narrator confesses. For almost 20 years and almost 20 plays, the best roles she has written have been invented “with Molly in mind.” Wandering through Molly’s house, the narrator attempts to parse what she can of her friend’s life outside the theater. By means of a few clues - a book, a table, a flood of morning light - the narrator situates us firmly in the past. Sometimes one memory “in turn triggered another memory,” she explains, “something that I had forgotten.”

The novel is structured as if the narrator were walking through a dark room, feeling the walls for a light switch. Nonetheless, it has form: the conflict, crisis and resolution are interior. It engages our attention and sympathy because the narrator wants to understand Molly. It is the intensity of the wanting that keeps us reading.

The turning point comes with the entrance of a minor character, a fan who has been so moved by one of Molly’s performances that she’s been inspired to ring the bell at Molly’s front door. This visit leads the narrator to a counter-intuitive epiphany: “that so much social interchange is inherently false, and real communication can only be achieved in ways that seem strange and artificial.” What better argument is there for art?