Chapter 1 is titled “An Unexpected Party” because Bilbo was not expecting Gandalf or the dwarves.
Gandalf stops by Bilbo when he is smoking. Bilbo is cheerful at first, and a little surprised to see Gandalf, especially after he tells Bilbo his name and Bilbo realizes he is a wizard. They have a strange conversation that starts friendly but turns almost rude, but he asks him to tea and Gandalf leaves.
Bilbo forgets about Gandalf until someone is at the door. It is not Gandalf, but a dwarf.
It was a dwarf with a blue beard tucked into a golden belt, and very bright eyes under his dark-green hood. As soon as the door was opened, he pushed inside, just as if he had been expected.
This dwarf is followed by more, and finally a laughing Gandalf. Bilbo gets more and more flustered and does not know what is going on.
He had made quite a dent on the beautiful door; he had also, by the way, knocked out the secret mark that he had put there the morning before. (ch 1)
Bilbo did not know that Gandalf was putting together a company to get a treasure from the dragon Smaug. He also did not know that Gandalf put a mark on the door so the dwarves would know where to find him, because Gandalf decided that Bilbo was going to be his “burglar.”
The dwarves have a good time, and use up Bilbo’s food. Bilbo is miserable. He does not want adventure, and the houseguests are chaotic. The dwarves find this funny and even sing about it, but they put the house mostly back together.