The "Bonus Goliath Chapter" is an extra chapter of Goliath written by Scott Westerfeld and posted on his blog on December 16, 2011. It includes one piece of art by Keith Thompson. The bonus chapter is located on the westerblog.  The bonus chapter takes place before and at a Zoological Society fancy dress party on New Years Eve and is from the point of view of Alek.
Originally, fans voted for a final piece of art by Keith Thompson , but Scott Westerfeld decided to post a story to go along with the art that was requested. He declared it canon when it was posted.
The bonus chapter begins with Alek and Count Volger preparing for a Zoological Society fancy dress party on New Years Eve in Alek's room at the Savoy Hotel, where the party will be taking place. Alek is going to wear a dress to the party, because he lost a bet with Deryn about an arm-wrestling contest between them. They had bet that the loser would wear a dress to the party, and Alek remembers that he made the wager because he wanted to see what Deryn would look like in a dress. Volger is going to dress as a message lizard, and has been "fortifying" himself for the party by drinking. Volger mentions that Alek now goes by "Mr. Hohenburg".
Alek and Volger talk about how fabricated animals can escape into the wild and destory the natural ecosystem. Alek is surprised that Volger would be worried about natural habitats, because he and Alek's father had killed so many deer when they went hunting.
Alek and Volger see Dr. Spencer, the director of the Zoological Society, dressed as a Huxley, and Dr. Barlow, her loris, and Tazza dressed as angels. Count Volger asks Dr. Barlow to dance, and Alek is left alone to find Deryn. He asks someone who is dressed as a gryphon if she is Dylan, but she is Adela Rogers. Adela Rogers asks Alek who he is dressed as, and he tells her that he is dressed as Ada Lovelace, a famous Clanker boffin from Great Britain. Adela Rogers tells Alek that she came to London to "do some follow up" about why he gave up his empire to work for the Zoological Society.
Wearing high heels makes Alek appreciates Deryn's ability to disguise herself as a boy. When he finally finds Deryn, he notices that she is also wearing a dress, one that is much more stylish than his. Bovril is also wearing a French style dress.
Deryn expresses her disappointment that Alek's dress is old-fashioned, and tells him that she just wanted to see him in something besides princely clothes. Deryn invites Alek to a "wee changing room" to which she has the only key with a bottle of champagne. The story ends with Bovril saying Mr. Hohenburg to Alek. The bonus picture follows the story.