Bilbo decides he can use the entrance to help the dwarves escape. The elves often send down empty barrels to go back to the human settlements. He can take advantage of this.

One evening there's a great feast in the cave. The king's butler and the chief captain drink some of the king's fine wine and fall asleep after. Bilbo can't believe his luck but acts quickly and takes the prison keys from the captain.

He lets out each of the dwarves, finishing with Thorin. Bilbo explains the plan of escaping down the river which the group doesn't like but they realize they have no other alternative and may not be so lucky as to get their hands on the cell keys again.

They make their way past the sleeping elves and crawl inside of empty barrels just in time before the group of elves tasked with pushing the barrels down into the river arrive. The elves wake up the sleeping butler and ask him if he's sure these are the barrels that are meant to go back to the men as they're a bit heavy. The butler assures them these are the correct barrels so they push them down into the river.

Bilbo was not in one of the barrels so he panics about what to do. In the end he grabs onto one of the last barrels and plunges into the ice cold water below. The elves close the trap door and leave him and his floating friends down in the dark waters.