This is a hot man on man steampunk romance of the science fiction mixed with fantasy type, set in a captivating world and driven by strange but likeable heroes and secondary characters. 
 The plot is simple and well executed. The mystery does not distract from the romance, and the romance is supported by an interesting mystery. The chemistry between the heroes is good, the sex is hot and their love story is very romantic, beautiful. 
 All through the book, I would wish it was a Tim Burton movie and I could actually SEE all the vivid descriptions of Purinton, Taintwell, the Mongrels and the "mechanical" circus. 
 I would picture young William with his red cheeks and unstoppable mouth trying to appear older, wearing his severe black and yellow coat and trousers, a yellow cravat tight around his neck, and selling his miracle potion in the circus, "brandishing a wand in one hand and a corked bottle in the other", and talking with a voice quite strong that obviously does not match his age but certainly attracts customers. A younger Johnny Depp will be a perfect Will. 
 And I would also picture Fanule Perfidor, the king of the man-beasts, 40% human and 60% something, abnormally tall, Abnormaly handsome, a bit insane and certainly more "human" than the "100% human" who govern the city. And Garou would be a perfect gentle, gorgeous and insane semi-alien giant (Garou is very tall canadian actor/singer who brilliantly played Quasimodo the hunchback in Notre Dame de Paris musical in France and sang with Celine Dion. Pics at http://www.polyvore.com/garou_as_quas... ) 
 As for the diabolical Hunzinger, I picture him with a huge tummy and a horrible mustache. And bad breath. And a green wart at the end of his nose like the Gruffalo. And lifeless eyes with dollar pictures. 
 This book was a nice trip to romantic-erotic steampunk land.