The team get involved when graffiti claiming 'I Killed Flak' appears around London, Flak being tag artist Danny Tyler, killed four years earlier. He was part of an artist collective the Maze Group which broke up when Danny received patronage to go solo from art lover Sir David Bryant, a fact which caused resentment from others in the group. Gallery owner Sara Hamlyn admits responsibility for the current graffiti, a publicity stunt for her Flak exhibition but draws the team's attention to a theft from her gallery of one of Flak's works before he died. The team are led to believe that Sir David stole it as he needed money and killed Flak during the resultant argument. Another ex-Maze group member Kevin Humphreys has been blackmailing Sir David as a result. But then Bryant's wife Catherine gives Sandra information which puts things in a different light. Brian has all the while been enjoying a following on Twitter as Top Cop 99, a fact which almost puts the case in jeopardy.