In Chapter V of The Great Gatsby, what does Nick find unusual when he comes home? How does his description contribute to the mood?

The chapter begins with Nick's describing what he finds when he comes home after leaving Jordan:

When I came home to West Egg that night I was afraid for a moment that my house was on fire. Two o'clock and the whole corner of the peninsula was blazing with light which fell unreal on the shrubbery and made thin elongating glints upon the roadside wires. Turning a corner I saw that it was Gatsby's house, lit from tower to cellar.

The contrast between Gatsby's huge house blazing with light and the darkness that surrounds it is striking. Nick's observation does not end there, however. He continues, his additional description serving to develop the scenic contrast:

At first I thought it was another party, a wild rout . . . with all the house thrown open to the game. But there wasn't a sound. Only wind in the trees which blew the wires and made the lights go off and on again as if the house had winked into the darkness.

Thus Gatsby's glowing empty mansion stands alone in the darkness, surrounded by silence, except for the wind moving through the trees. The mood is one of loneliness and isolation, with a certain sense of eeriness as the lights blink off and on. Gatsby is clearly alone, in more ways than one. This idea is emphasized a few paragraphs later, after Nick has had a brief conversation with Gatsby and ended the evening. Nick comments he does not know how Gatsby spent the rest of the night:

I think I walked into a deep sleep as I entered my front door. So I don't know . . . for how many hours he "glanced into rooms" while his house blazed gaudily on.

The image of Gatsby wandering through his empty mansion, looking into empty rooms, is both moving and symbolic of his life.