My Mortal Enemy by Willa Cather is a 105-page paperback, Vintage Books, a division of Random House, New York, first published in 1926.  I am unsure when this copy was published.  There is tanning around the page edges.   

Book Summary

My Mortal Enemy is one of the most powerful, as well as one of the sparest, of Willa Cather's novels.  It is, as her biographer E.K. Brown wrote, "the novel stripped of its superfluous furnishings."  The story of Myra Henshawe, a worldly woman who gives up a fortune to marry as she chooses, and then finds that her romantic gesture has not brought her happiness, is told with an economy as extraordinary as its insight.  And Myra's ultimate revelation of who her "mortal enemy" is still has the power to shock.  First published in 1926, the book has been a favorite with readers and critics ever since.