Agent 21: Codebreaker

Special agent Zac Darke is back for his third mission—and the stakes have never been higher. An unknown bomber is conducting a terror campaign in London. After an explosion on the tube leaves someone dead, Zac and his team are brought in to try and work out how this terror cell operates—but clues are scarce and they have no idea where, or when, the bomber will strike next. A teenage boy, currently detained in a young offender's institute, claims he has the answer—but before Zac can question him, the boy is shot and falls into a coma. Will Zac be able to break the cipher before the bomber strikes again?