The police inspector of the traffic unit, TO CHEUK-FUNG (Kenny Wong), takes it upon himself to crack down on illegal street racing and bring the criminals to justice, often driving a stealth car to patrol the highways for traffic enforcement along with his subordinates. CHEUK-FUNG appears to be an aloof man with a stern face, and none of his co-workers understand him except SZE MA (Benjamin Yuen) of the accident investigation unit. Just as everybody is certain that rookie BEI SAM-JOU (Sisley Choi), a girl with an outgoing, bubbly personality, will not go through the rigorous training by CHEUK-FUNG, to their surprise, SAM-JOU and CHEUK-FUNG thus develop a father-daughter-like mentorship. On top of that, SAM-JOU even helps CHEUK-FUNG get over something that he has been dwelling on. Watching with envy, SZE MA tries to persuade SAM-JOU to join his team because the performance of his subordinate, YIU YIU (Natalie Tong), is below expectation.
SZE MA is very thorough and always makes straightforward cases more complicated than they need to be; whereas YIU YIU, by contrast, runs things by the book and is constantly at daggers drawn with SZE MA. With street racers once again rampaging through the town to publicly provoke law enforcement, CHEUK-FUNG deploys his team to launch a traffic campaign against illegal street racing, without knowing that he is instead brought to the brink of catastrophe. Meanwhile, the dark cloud that had overshadowed CHEUK-FUNG for many years re-emerges..