Cirque du Freak: The Vampire's Assistant

Darren Shan and his best friend Steve Leonard visit a traveling freak show. Steve believes a performer, Larten Crepsley, is a vampire. Steve talks to Crepsley after the show and asks to become a vampire. Crepsley initially refuses but is talked into testing Steve's blood, that he spits out telling Steve he has bad blood. Steve furiously swears revenge and leaves. Darren overhears everything because he has been hiding in a cupboard after stealing Crepsley's spider, Madam Octa.
When Crepsley realizes that Madam Octa has been stolen, Darren flees from the theater with Crepsley hot on his trail. Outside there is a limo waiting for him, which he is told to get into. Inside he meets Desmond Tiny and mad Vampaneze Murlough. They drop Darren off at his house where he sneaks back into his room.
At school Darren is looking at Madam Octa. Steve sees him and grabs the cage to look too. Madam Octa jumped at Steve while he was holding the cage to look at it, startling Steve and making him drop the cage and it escapes. After a chase by Steve and Darren Madam Octa slips into Steve's shirt, bites him, and makes good its escape. Madam Octa's poisonous bite leaves Steve in the hospital. Darren asks Crepsley for the antidote. In exchange for an antidote Crepsley requires Darren become a half-vampire and Crepsley's vampire assistant. Darren agrees, but after Crepsley gives Steve the antidote Darren reneges on his promise to become his assistant. Later, thinking of feeding off his sister, Darren agrees to leave his family and join Cirque Du Freak as Crepsley's assistant. Darren fakes his death and a funeral is held for him.
When Crepsley digs up Darren's grave they are attacked by Murlough who wants to make Darren a Vampaneze. After winning the fight Darren and Crepsley return to Cirque du Freak where Darren meets the snake boy, Evra Von, and Rebecca, the monkey girl. Meanwhile, Steve, still attempting suicide, is stopped by Mr. Tiny who offers him a chance to become a Vampaneze, like Murlough. Mr. Tiny tells Steve that he is neither a vampire nor a Vampaneze, but someone with an interest in both. Tiny learns Darren has not fed on humans yet and sends Vampaneze after him, knowing that he will be weak. Darren escapes, so they kidnap Rebecca and have Evra tell Darren to "come home".
Mr. Tiny makes contact with Steve and entices him to join his Vampaneze by playing on his resentments and insecurities. Steve is turned into half-Vampaneze and then he and Murlough capture Darren's family. Darren arrives home to find his family missing and a flier for Cirque du Freak. Darren arrives at the theater, where Murlough and Steve are waiting for him. They fight, but Darren is weak from not feeding.
Crepsley arrives to fight Murlough. Rebecca frees herself, while Mr. Tiny watches from the balcony. Rebecca offers Darren some of her blood. He eventually agrees and fights with Steve using his new powers. Crepsley stabs Murlough and with his dying words Murlough declares that the truce between the two clans is broken. Steve and Darren continue to fight, but Tiny stops them and turns Murlough into a Little Person. Tiny and Steve then leave.
Darren's family are hypnotized to have forgotten what happened to them. Left by themselves, Rebecca and Darren then share a long heartfelt kiss before being interrupted by Mr. Crepsley. Crepsley gives Darren his own coffin, and Darren accepts his new life as a member of the Cirque du Freak.

Question: What has been stolen?
Answer: Madam Octa