Dragon Detective: Schools Out! by Gareth P. Jones

"The Dragon Detective Agency. Dirk Dilly speaking."Holly is desperate to be sleuthing with her partner-in-solving-crime, dragon Dirk Dilly, but instead she's stuck at her exclusive boarding school for children of the rich and famous. She's determined to escape, until she meets Callum, the son of the Prime Minister, who claims he was kidnapped by dragons a year ago and hasn't been the same since.

And when Dirk's own investigation into dragon activity brings him to the school, the two cases collide. What if Callum isn't as crazy as he seems?