The Fall of Gondolin

Gondolin, beautiful but undiscoverable, is central to the enmity of two of the greatest powers in the world. Morgoth of the uttermost evil seeks in vain to discover the marvellously hidden city of his Elven enemies, while the gods in Valinor refuse to support Ulmo, the Lord of Waters, and his designs to protect it. Into this world comes Tuor, cousin of Túrin, and guided unseen by Ulmo he sets out on the fearful journey to Gondolin to warn them of their coming doom.
Then Morgoth learns through an act of supreme treachery all that he needs to mount a devastating attack on the city, with Balrogs and dragons and numberless Orcs.