After he's caught stealing drugs from evidence, Aidan Waits is blackmailed into an undercover operation which sends him from the upper echelons of the super-rich to the low-life squalor of Manchester's drug scene. He spends his nights tailing The Franchise, a sophisticated gang operating out of the city's booming bar culture, but when David Rossiter, a powerful member of parliament, discovers that his runaway teenage daughter has turned up in their custody - everything changes. Isabelle Rossiter has joined the dangerous world of the sirens, the young women who go from bar-to-bar collecting drug money for The Franchise. Each lives in the shadow of Joanna Greenlaw, who cut a deal with the police then vanished without a trace. As Franchise members begin to die, and a toxic strain of their designer drug hits the market, it becomes clear that someone doesn't want Joanna Greenlaw to be forgotten.