The Thames-Tigris Connection

Metropolitan Police Detectives, Vance and Shepherd, are investigating a case in Central London. Several murders of prominent Iranian exiles present Vance with a powder-keg primed to explode.
He and Shepherd must avoid a conflict among London's Muslim community. MI-6 involvement results in the arbitrary closure of three unsolved cases, however, the Intelligence Agency has a plan for Shepherd - to make use of her ability as a renowned crack shot.
But can they discover and take down the fanatical anti-Zoroastrian movement in Tajikistan, Afghanistan and eastern Iran, and at the same time provide justice to the victims of the closed cases?