Following the collapse of KMG (Keith Moore's Gang) at the end of James' Second mission, rival drug gangs the Mad Dogs and the Slasher Boys engage in a violent turf war for control of the Luton underworld. CHERUB agents Gabrielle O'Brien and Michael Hendry are sent to infiltrate the Slasher Boys. While carrying out a delivery for Major Dee, the leader of the Slasher Boys, Gabrielle's contact is killed by members of rival gang the Runts and Gabrielle is grievously wounded after being stabbed by a Runt.