Literary biography is never finished, Hermione Lee, the Goldsmiths’ professor of English at Oxford and author of acclaimed books about Virginia Woolf and Edith Wharton, said the other day. New information keeps turning up. In the case of Wharton, what has just turned up is a letter that casts new light on the vexing question of what exactly happens at the end of her 1905 novel, “The House of Mirth.” Does Lily Bart, the novel’s heroine, kill herself or die of an accidental overdose?

The text is ambiguous. Lily, honorable but not always smart in her decisions, has so fallen from her perch in New York society that she is living in a boarding house, and so broke that she needs to work for a living. She has quit one job, as secretary to a tasteless social climber, and has failed miserably at another, sewing for the fashionable milliner Mme. Regina, and to get through the nights has become addicted to chloral hydrate....

The newly revealed letter, written by Wharton herself, seems to point to the suicide theory. It is dated Dec. 26, 1904, or just a month before “The House of Mirth” began appearing in monthly installments in Scribner’s Magazine, and is addressed to Dr. Francis Kinnicutt, a well-known society doctor who specialized in the mental ailments of the well-to-do. At the time of the letter, in fact, he was treating Wharton’s manic-depressive husband, Teddy, who was beginning to behave in ways — eventually embezzling her money, setting up a mistress in Boston — that would lead to the dissolution of their marriage.