What is the Central theme of the book Cirque du Freak A Living Nightmare?

Okay, so Darren Shan is just an ordinary boy, but then his life changes when he goes to a freak show(Cirque du Freak). He goes to this freak show with his friend Steve. So they go and see all of these freaks. But then Mr. Crepsley goes onstage and he has a cool spider (Madam Octa) who you can control with your mind if you really concentrate and have a Flute. Darren really likes Madam Octa, but then Steve sees Mr. Crepsley and gets really scared. After the show, Darren hears Steve asking Mr. Crepsley to turn him into a vampire, and Darren find out that Mr. Crepsley is a vampire! Then Mr. Crepsley tests Steve's blood and says that he has terrible blood and that he is evil >:( . Well, anyway, after some days, Darren still loves the spider and finally steals her from Mr. Crepsley! After a while, Darren wants to show the spider to Steve and does. That's when the real trouble begins. The spider gets on Steve's neck and Darren tries really hard to concentrate and makes sure that the spider doesn't do anything to Steve, but then Annie (Darren's little sister) comes in being loud, Darren stops concentrating, and the spider bites Steve. It only takes two bites to kill someone and the spider is ready to go for the second bite, but Darren takes the spider. Darren doesn't want to tell anyone about the spider because his parents don't let him have Spiders, so he tells his mom that he went to the bathroom and that when he came out, he was a paralyzed. So then they take him to the hospital, but the doctors can't find out what's wrong, so Darren goes to talk to Mr. Crepsley. He asked him if he had a cure, and he did, but Darren has to do something in return for him. He has to becomes a vampire's assistant. Darren accepts. So Darren becomes a half-vampire, and he and Crepsley go to the hospital and put the medicine on Steve, saving him just in time. Then Darren makes a run to the door because he doesn' t want to go with Crepsley. But then the next day he sees differences in himself like that he wants blood and can't sleep. So he goes back with Mr. Crepsley and they fake his death. Then Mr.Crepsley goes to the graveyard where they buried Darren and he digs him up. They both go on and Darren has a new life as a vampire's assistant.