Murder. Abduction. Two cities. Two cops... Eighteen months ago. Chinatown, London. A police raid goes disastrously wrong. People die. Today, those police officers involved in the swoop are dead. Serial, Purple One Five, are all dead, except the serial commander - Sergeant Brian Gibson.

In Hong Kong, a woman's body is discovered in a seedy downtown Wan Chai hotel. Detective Inspector of Police Mandy Lee must determine who she is and who killed her. Lee identifies the woman as Andrea Ventress-Gibson. Lee's investigation leads her to the UK, but Andrea's new husband, Sergeant Brian Gibson, is missing - whereabouts unknown. Meanwhile, in the UK, Road Policing Officer PC Ed Roberts discovers a cyber-attack on a police database. But he's ordered to chaperone D. I. Lee. As a team they soon find that their enquiries are linked.

Against orders, Roberts follows Lee to London's Chinatown, where they come into direct conflict with a Hong Kong underworld organisation - Crimson Dragon. And confirms Lee's suspicions her estranged step-brother is involved. Can Lee and Roberts discover Gibson's whereabouts and stop Crimson Dragon?