The film's 'hero' is a tough anti-terrorist officer, played by singer Emil Chau. His character, Mark Chan, is every bit as ruthless in his determination to foil a diabolical terrorist plot.

The villain of the piece is Soong, is played by Kam Kwok-leung. Kam, a familiar figure in Hong Kong show business circles, is now virtually unrecognisable with blonde hair and goatee and odd-coloured contact lenses. He looks really cool, and remember to check out his 'New York look'.

The man he plays is similarly deceptive, a charismatic revolutionary prepared to achieve his goals of Pol Pot's agrarian society at any cost. The Purple Storm refers to a biological warfare, a chemical called Risin-X, which the terrorists plan to unleash with the coming monsoon storm. Its chemical reaction when unleashed will turn all that it comes in contact with purple and will render absolute death in less than two hours.

At the centre of the action is Todd, played by model-turned-actor Daniel Wu. Wu has abandoned his teen idol looks for a close-cropped hairstyle, a look that accents his lean angular features. He plays a Soong's son, Todd, who suffers from amnesia and is in the custody of Chan. Chan deceives him that he is in fact an undercover agent assigned to infiltrate Soong's terrorists group to uncover Soong's diabolical plans.

Joan Chen, cast in so many Hollywood productions as a femme fatale, is Dr Shirley Kwan, a sharp professional woman who drives a swanky silver convertible, as psychiatrist who develops more than a clinical interest in the man placed under her care. She lends a regal presence and calm to a choatic world as seen through the eyes of Todd.

Todd, having been presented with a chance for a new life, complete with an apartment and even a girlfriend (there are some light moments here), is torn between the memory flashbacks that he suffers and a promising new life. He is torn between his loyalty to his father and doing what he believes is right, even though his new life turns out to be a lie.