When Nina returns to work after recovering from a near-fatal injury, she's supposed to be keeping her head down. But the cold case she's working on - an infamous train crash from 1964 - is no match for the lure of the shootings, drugs deaths and robberies keeping her colleagues busy. And before long she uncovers crucial new evidence linking the historic crash to the current spate of heroin-related deaths. Once again, she's back at the centre of a complex case which brings her face-to-face with a network of criminals who will stop at nothing to protect their empire.