Nienna's Gift is a gen 49-page Lord of the Rings novel by Sheila Paulson.
From a distributor, Agent With Style: "Deprived of his memory but miraculously gifted with his life, Boromir awakens in a small Rohan village and begins the journey to recovery from his fatal wounds, in this fascinating novel prequel to Honor... While the shadows of Sauron intensify, he wins back to strength, knowing there is something in his past he is glad to forget. But memories tantalize him even as he rides to battle on the Pelennor Fields in Rohan armor under another name. Will he find his identity, his purpose, hope for the future, forgiveness — not only from the one he most wronged, but also from himself?"