Silmarillion Blues : Quenta Silmarillion : VIII. Of the Darkening of Valinor

For a time Melkor avoids those hunting him, still empowered with the ability to change shape or pass unseen.  Meanwhile, Ungoliant, a creature of whom her origins are wondered at by even the Eldar, made her home within Avathar, taking on the form of a giant spider, and consuming any Light that fell within her grasp and spinning it out into shadowy webs.  Ungoliant is the progenitor of the Spiders we meet throughout The Hobbit and The Lord of the Rings, Shelob and her ilk, dark creatures in spider form that are burned by blessed Light.  Melkor seeks her out, taking on his guise of a Dark Lord he bore in Utumno, a form in which he remains, and strikes a deal.  "Do as I bid; and if thou hunger still when all is done, then I will give thee whatsoever thy lust may demand."

Under a cloak of darkness woven by Ungoliant, Melkor strikes at Valinor in the midst of a celebration of thanks giving and forgiveness.  Fëanor comes in simple presentation, and reconciles with Fingolfin before the throne of Manwë.  Manwë, the Valar, and the Eldar may have wished for a sight of the Silmarils that Fëanor left locked in Formenos, but the triumph of Melkor would have been more complete had he brought them.  Melkor strikes down both Trees, and Ungoliant drains any vitality they hold into herself, and then the Wells of Varda, growing and swelling so large that even Melkor fears her.  And so darkness falls on Valinor, a darkness imbued with living shadows as our antagonists leave, their vengeance complete.

Troy closed his post off with Voltaire, but I'm going with Blue Oyster Cult, and making a Career of Evil (it was that or Skull Crusher Mountain).