| Cast overview, first billed only: | |||
| Leon Lai | ... | Lai Soeng-Zing | |
| Ekin Cheng | ... | Lee Man-Kin | |
| Francis Ng | ... | Au-Yeung Hoi | |
| Karena Kar-Yan Lam | ... | Brenda (as Karena Lam) | |
| Jinglei Xu | ... | Mandy Cheuk (as Jing Lei Xu) | |
| Raymond Ho-Yin Wong | ... | Officer Yeung (as Raymond Wong) | |
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Rico Kwok | ... | Zhi |
| Anson Leung | ... | Tom | |
| Samuel Pang | ... | Chi | |
| Hing-Yin Kam | ... | Commander Wong | |
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Cheung-Ching Mak | ... | Commander Lau |
| Tak-Bun Wong | ... | Cheung Kwok-Leung | |
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Ho-Sun Lee | ... | Wong Man-Kit |
| Frank Michael Liu | ... | A Team (as Chung Kei Lau) | |
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Ming Nam Po | ... | A Team |
Ken Lee dated girlfriend Brenda but the love isn't strong enough. Jack Lai married Mandy (Chui Jing Lui), police friend (Wong Tak Ban) killed by Jack's boss. Jack was a professor of a University, but his busy work makes Jack to neglect Mandy. One day, Jack's friend came to his home and wish to rape Mandy, Mandy killed him. Jack returned to home, Mandy cried why can't he always appear to herself when she need him. Jack admitted that the man was killed by him so that Mandy became innocent. But Jack's boss caught Mandy. Grace, widow of Jack's police friend, with her two children, were locked with Mandy. Jack taught the criminals with psychology in his jailed period. One day, Ken visited the criminals and met Jack. Jack told Ken to treasure his lover. Jack drew a picture to Ken, which was sunset and sea, but it was drew specially in SOS sign. Ken didn't understand Jack when he got Jack's picture. Jack told Ken about his own boss who capture Mandy from him, and Ken brought his crew members... Written by Pete_Sampras
Although this film received very little or no attention upon its release,even allowing for its minor shortcoming, I'd still rate it among the best movies I've ever seen. Take The Usual Suspects and The Sixth Sense, combine the two movies and throw in a little action and some seriously nerve-wracking, tense "heartless" villainy and you have Heroic Duo. One complaint: the weak title doesn't do this film justice. I still have to give it a ten-star rating. I know, you've never even heard of it, but compare it to the critically acclaimed Infernal Affairs (which I believe to have been highly overrated) and see what I mean.