Guardian Angel: Book 14 by Robert Muchamore
Guardian Angel is the second book in a brand-new CHERUB series from Robert Muchamore. Ryan has saved Ethan's life more than once. Ethan thinks he must be a guardian angel. But Ryan works for CHERUB, a secret organisation with one key advantage: even experienced criminals never suspect that children are spying on them. Ethan's family runs a billion-dollar criminal empire and Ryan's job is to destroy it. Can Ryan complete his mission without destroying Ethan as well? For official purposes, these children do not exist.