How does Thorin react when he discovers that the Arkenstone is now in the hands of his enemies?

When Thorin becomes aware that Bard is in possession of the Arkenstone, he becomes angry and filled with rage. He threatens to throw Bilbo on the rocks and accuses Bilbo, Gandalf, and the dwarves of conspiring against him. Thorin readies himself for war. 

"You all seem in league!" said Thorin dropping Bilbo on the top of the wall. "Never again will I have dealings with any wizard or his friends. What have you to say, you descendant of rats?"