You're resting in the Shire with your old friend Bilbo Baggins when a knock comes from the door. You open it and to your surprise twelve dwarves walk in. Behind them is the wizard Gandalf who explains that they've all come for your help.

The most prestigious dwarf, Thorin Oakenshield, speaks for the group and tells the tale of how his people were forced to flee the ancient dwarven stronghold of Moria and journey to a new home in Erebor, the Lonely Mountain of the East. There they lived in exile until a great dragon, Smaug the Terrible, appeared and ransacked the mountain, killed its inhabitants, and rested inside on his hoard of stolen treasure.

Now two hundred years later, the dwarves are ready to retake their home and wish you to join them (and share the treasure). You and Bilbo both accept their offer. Before you set out, Gandalf shares with Thorin a map of the Lonely Mountain and a key to a secret entrance.

Details at Eamon Wiki