Skulduggery Pleasant - book 1
 
Meet the great Skulduggery Pleasant: wise-cracking detective, powerful magician, master of dirty tricks and burglary (in the name of the greater good, of course).
Oh yeah. And dead.
Then there's his sidekick, Stephanie. She's... well, she's a twelve-year-old girl. With a pair like this on the case, evil had better watch out...
So you won't keep anything from me again?"
He put his hand to his chest. "Cross my heart and hope to die."
"Okay then. Though you don't actually have a heart," she said.
"I know."