That's a shame. Is that book apart of middle earth?
You'll see...
Tolkien deeply loved two things (after God and his wife): languages and myths. He wanted to craft new languages for his own amusement (he honestly thought no one else would be interested), but he thought that those languages needed being talked by someone to look real. So he began to create a world -inspired by European myths- inhabited by the people would talk his imaginary languages.
So in 1917 he began to write a body of fairy tales, myths and legends he would call The Silmarillion. His intent was creating a legendarium of interconnected legends, some more elaborated and some more ambiguous and short. The three most important stories of that legendarium were "Beren and Luthien", "The Children of Hurin" and "The Fall of Gondolin".
Unfortunately he was a perfectionist prone to constantly to change his mind, restart again, rewrite a legend halfway only to leave it unfinished and start to rewrite another tale... Really, it is a miracle he got to publish The Hobbit and The Lord of Rings in his lifetime.
After his death, his son Cirstopher gathered part of his father's materials and drafts in a somewhat coherent mass and published The Silmarillion (the history of First Age, thousands of years before the events of The Lord of Rings), guessing that was NOT The Silmarillion his father intended to publish.
Unsatisfied with it, Cristopher decided to publish several series of books (Unfinished Tales, the Road Ever Goes On, The History of Middle-Earth...) in order to show a more complete image of the world his father had created.
Later, he considered one of the main legends was developed enough to be published. So he gathered and compìled several scattered notes and texts and published The Children of Hurin book.
I hope I helped you. If you want more information, you can check this link:http://tvtropes.org/...iensLegendarium