The Graveyard Riddle by Lisa Thompson: Signed bookplate copy
"An old, abandoned house hides a secret within its walls...
When Melody Bird meets the mysterious Hal, he tells her he's an undercover spy, keeping tabs on a gang of jewel thieves. But can a young boy really be in charge of such a dangerous mission?
Melody is determined to decode the strange riddles hidden in the graveyard, but Matthew and Jake wonder whether Hal is the true puzzle to be solved...?"