Celebrated graffiti artist Danny "Flak" Tyler was murdered four years ago . So why is "I Killed Flak" graffiti suddenly appearing around London? While the ream focuses on Flak's former crew members, Brian's obsession with Twitter proves distracting

`When the team receives new information about a fatal fire, they are drawn into a dangerous criminal underworld. The original investigation was blocked by a wall of silence, which may be crumbling--if a witness can be trusted.