The "extra scene" is nothing really big - highlight the next bit of text to see it...
(SPOILER)It's another scene during the play, "I want to be your canary", as performed by Tantalus. Leo is talking to Blank, who has just boasted about betraying Marcus. Leo is enraged that Blank would do such a thing to his friend; he probably realises that Blank murdered his daughter, too. Leo kills Blank, whose final words are that he merely sought a lasting peace between the kingdoms.
So, that's about it.