Ungoliant's many eyes gloated upon the gems that Melkor had shown her, and he told her of his diabolical plan. But when all was told, she was torn between lust and great fear, for she feared the Valar even more than the hatred of Melkor. And so Melkor said to her: ''Do as I bid, and if thou art still hungry when all is done, then I will give thee whatsoever thy lust may demand. Yea, with both hands.'' Of course he lied, and had no intention of keeping the promise. Indeed he would deliver her to the Valar to escape himself if he were in peril of capture.
There are many conflicting accounts given of what happened next; the one in The Silmarillion is succinct and a tad boring, but since this is supposed to be a synopsis of those tales, I shall (now!) remain faithful to what they say. A cloak of darkess Ungoliant spun forth to conceal them, an Unlight which was void, and they left that cleft in the mountains besides the dark sea and they scaled Hyarmentir, the highest mountain in that region, and at last reached its summit. Then Melkor looked forth and his eyes passed over the beech woods of Oromë, the green fields of Yavanna, and eventually he beheld the city of Valmar and the Two Trees, Laurelin and Telperion, the Gold and Silver. Then he laughed aloud, and leapt from that high place into the valleys below, and with Ungoliant he made northwards with great speed.
Meanwhile the Valar, Maiar and the Eldar of Tirion were upon the Holy Mountain within the Halls of Manwë and Varda, or upon the green slopes of the mountain, and they were singing and dancing and praising God, seeing no end to their mirth. It is said that even as Fëanor and Fingolfin were reconciled before the Throne of Manwë, Melkor and Ungoliant came hastening over the fields of Yavanna. And at last they came to the green mound Ezellohar, and Melkor sprang upon the mound. Then, he brandished his great black spear, and with it he pierced each Tree to it's core, and from the Trees there came forth sap, as it were their blood, and Ungoliant went from Tree to Tree and sucked them dry, and her poison went into the Trees and withered them, and they died. Meanwhile, Melkor went forth from the Trees and came to the places of his humiliation with vengeance, and he was back with triumph, Lord of Utumno, a monstrous misshapen spectre of Hate, and he defiled the Judgement seat of Manwë, and he threw down the thrones of the Valar, and he cursed the Ring of Doom. Then, whilst Ungoliant drained the Wells of Varda, he escaped in secret, making for Formenos, but she espied him and came after him in the growing darkness, and Melkor was aghast, for she had swollen to a shape so monstrous that he was afraid; but he could not contend with her, even if time allowed, without aid.
Thus the land of Valinor foundered in the Unlight, indeed the Blessed Realm now shared in the darkness of the World. The Silmarillion has this to say of what followed:
''So the great darkness fell upon Valinor. Of the deeds of that day much is told in the Aldudénië, that Elemmírë of the Vanyar made and is known to all the Eldar. Yet no song or tale could contain all the grief and terror that then befell. The Light failed; but the Darkness that followed was more than loss of light. In that hour was made a Darkness that seemed not lack but a thing with a being of its own: for it was indeed made by malice out of Light, and it had power to pierce the eye, and to enter heart and mind, and strangle the very will.
''Varda looked down from Taniquetil, and beheld the Shadow soaring up in sudden towers of gloom; Valmar had foundered in a deep sea of night. Soon the Holy Mountain stood alone, a last island in a world that was drowned. All song ceased. There was silence in Valinor, and no sound could be heard, save only from afar there came on the wind through the pass of the mountains the wailing of the Teleri like the cold cry of gulls. For it blew chill from the East in that hour, and the vast shadows of the sea were rolled against the walls of the shore.''
Then Manwë looked north and east from his lofty halls over the Sea and he saw the Unlight hastening, and he knew that Melkor had come and gone. But the pursuit was unavailing. Melkor had come and gone, and his vengeance was achieved.