LAU CHUEN HUNG, his sister CHUEN FONG and their friend CHEUNG HO NAM are taken hostages by robbers on a mini-bus. Being bold and daring, NAM tries to deal with the robbers and eventually helps the police to arrest the robbers. This wins him praises from the Police Inspector LEE TAT FOK. Encouraged by FOK, HUNG, NAM and their friend CHENG SING attempt to join the police force. In the end, WAM and SING are admitted but not HUNG who gets infuriated and perplexed.

Later, HUNG finds out that the reason for his failure is due to his father's connection with the underworld. Feeling disappointed and angry, he quarrels with his father KUEN. NAM's sister NG dislikes NAM being a police and asks him to quit the job. It just happens that FOK has asked NAM to act as a secret agent to crush a case. So NAM lies to his aster that he has left his job and this delights NG. With the help of his partner, NAM starts working for the underworld but is discovered by HUNG. Having to keep his real identity a secret, misunderstanding arises between NAM and HUNG. This greatly disturbs NAM who is determined to crush the case as soon as possible. Also, from his partner he learns that the life .of a secret agent is in no way an easy one. At the same time, NAM gradually gains the trust of the ringleader.

NG finally gets married and immigrates to Canada. Sadly she says goodbye to all her loved ones in Hong Kong. KUEN thinks that NAM is in financial trouble and so driven to work in the underworld. So he lends money to NAM who is greatly impressed. At the same time, KUEN and HUNG finally reconcile and come to a better understanding of each other. NAM and his partner help the ring-leader in a robbery. When they are celebrating their success, the ring-leader accidentally discovers the real identity of NAM's partner and tries to kill him. NAM attempts to save his partner who finally kills himself so as not to get NAM endangered. His partner's death makes NAM determined to avenge for him.

Upon their success in the robbery, NAM urges the ring-leader to sell the loot to another gang, hoping that through this he can get both gangs arrested. At first, the ring-leader refuses to follow NAM's suggestion. After much work done by NAM, the ring-leader finally gives his consent. NAM informs FOK of the meeting place of the two gangs. Eventually, both gangs are all arrested. FOK appreciates much NAM's courage and efficiency. He recommends him to join the flying squad. Encouraged by NAM, SING also applies and both of them get admitted. NG suddenly re turns from Canada because her marriage breaks. KUEN offers her much consolation and advice. One day, NG faints after taking the wrong medicine. KUEN sends her to the hospital thinking that she attempts suicide. In the meantime, NAM gets so involved in his work that he cannot get the time to visit NG and misunderstanding arises between KUEN and NAM.

In the flying squad, NAM and SING get acquainted with another group headed by COOL. The two groups do not get along well with one another. COOL often makes fun of NAM who tolerates his ridicule with patience. SONG, an enemy of KUEN, returns from Holland to avenge on KUEN for his former betrayal of him and his brother, victimizing them to become prisoners for years. SONG blackmails KUEN who promises to pay him in order to make up for his own fault. However, SONG kills KUEN after getting the money. KUEN's followers want to take revenge for KUEN and chase after SONG. Having got hold of the cremated remains of KUEN's body, SONG forces HUNG to negotiate with him. Being ridiculed by SONG, HUNG loses his senses and kills SONG.

In order to avoid trouble, HUNG takes refuge on Lantau Island. A former follower of KUEN, CHUNG, now takes over KUEN's place. The gap between NAM and COOL widens. Enmity even breeds when the two of them strive to become leader in the flying squad. Later, NAM is attracted by a beautiful police inspector LEE KIKI whom COOL claims to be his girlfriend. COOL even stops NAM from courting her. On the contrary, this makes NAM even more determined to win her heart. On learning that NAM starts dating with KI, COOL gets infuriated and this deepens their hatred for each other.

In many trials, NAM proves his capability and is finally chosen as leader of the flying agued. This makes COOL both disappointed and angry. On the other hand, NAM wins FOK's appreciation and praises when he crushes a case and successfully saves KI's life. HUNG feels tired of being engaged in illegal business. Yet CHUNG refuses HUNG's suggestion of stopping the business and HUNG feels unhappy about this. By chance, HUNG runs into ANITA who leaves a deep impression on him. KI is commanded to crush the underworld gang headed by HUNG. Knowing that HUNG and NAM are good friends, she tries to get closer to NAM. As time goes by, love breeds between KI and NAM. On the other hand, SING starts dating with FONG who secretly admires NAM and shows no interest in SING.

Discovering the love between KI and NAM, both COOL and FONG gets disillusioned. Being unable to settle her debts, ANITA is beaten but is saved by HUNG and she gradually grows fond of him. SONG's brother returns to Hong Kong and is determined to avenge on HUNG. He causes much trouble which affects HUNG’s business. In order to pacify SONG's brother, HUNG tries to, negotiate with him. However, he is ridiculed and made fun of by SONG's brother. On seeing HUNG's inability in resisting, CHUNG feels eager to leave HUNG and joins SONG's brother.

ANITA warns HUNG of GHUNG being disloyal to him. On the one hand, HUNG grows suspicious of CHUNG while SONG's brother tries to persuade CHUNG to join him. By accident, FONG learns of their plot to kill HUNG. However, before she can inform HUNG of that, she herself is caught. SONG's brother decides to sell her to Japan as prostitute instead of killing her. Fortunately, she is saved by the flying squad headed by FOK. Through this incident, she learns that both NAM and SING are members of the squad. The enmity of the two gangs intensifies after FONG's disappearance and CHUNG intends to do away with HUNG. However, ANITA comes to HUNG's rescue even risking her own life. In the end, both of them are saved by HUNG's followers.

SONG's brother comes into open conflicts with HUNG. The two gangs exchange fire and accidentally kill an innocent citizen. Under pressure from the public, the police seeks help from the flying squad and forms a special commission headed by FOK and KI to crush the two gangs. Mixed feelings swell in NAM's heart when he learns that HUNG is involved. FONG is sad to discover that NAM and KI are deeply in love. She is taken to drinking and once when she is drunk, she discloses to HUNG that NAM is a member of the flying squad. HUNG is shocked to discover that and he tries to persuade NAM to give up his job and join him. However, NAM declines his offer. Again SONG's brother plots to kill HUNG. ANITA helps HUNG to escape and she herself is kidnapped.

SONG's brother uses ANITA's life to threaten HUNG to join him in drug-trafficking. In the end, the two gangs promises to cooperate in the illegal business. The love between HUNG and ANITA grows deeper after all these incidents and they decide to co-habituate. In order to get rid of SONG's brother, HUNG betrays him by telling NAM the meeting place between SONG's brother and the drug- trafficker. The flying squad is commissioned to crush the whole gang but SONG's brother manages to escape. NAM is seriously injured when he tries to save COOL from danger and is taken to the hospital. HUNG lies to the drug-trafficker that it is SONG's brother who betrays him. The drug-trafficker vows to avenge on him and promises to cooperate with HUNG. Being urged by HUNG, NG warns KI not to go out with NAM but KI refuses to listen to her. In order to avoid further misunderstanding, NAM honestly tells FONG that he only looks upon her as his sister……

KI's love for NAM remains unaffected by this incident. However, FONG feels so hurt that she attempts suicide but is saved by NG. NAM feels very sorry for her and guilty feelings swell in his heart. SING has all along secretly admired FONG and now he plucks up his courage to declare his love for her. Encouraged by ANITA, FONG resolutely accepts his love and marries him. HUNG asks SING to quit his job and helps him in his business. In order to relieve FONG of worrying for him, he leaves the squad. HUNG plots to assassinate SONG's brother who manages to escape and cooperates with the police to appear as witness giving evidence against HUNG.

HUNG is arrested and he claims that SONG's brother is making false charges against him. NAM does not believe his words but SING and FONG fully trust him and worry much for him. NG also believes that HUNG is innocent. She urges NAM to help! HUNG but NAM refuses. She gets infuriated and refuses to see him. The followers of SONG's brother decides to avenge on HUNG. They try to assassinate HUNG but he is saved by NG who dies. To vent his sorrow over his sister's death, NAM beats SONG's brother who in the end gets angry and refuses to appear as witness. NAM has no alternative but to apologize to him so as to seek his help. Knowing that the evidence is against him, HUNG sends his follower to get rid of SONG's brother. In the end, because of insufficient evidence, HUNG is released.

HUNG gradually gains his power in the underworld. ANITA gets pregnant and they get married. HUNG asks SING to help him in his illegal business but SING refuses. ANITA runs into her former love WONG HO who is the leader of a gang of robbers. HUNG gets their help and uses their loot to buy drugs. The series of robberies arouse the attention of KI and FOK. They suspect that HUNG is behind these and they probe into the case. SING is shocked to discover HUNG being engaged in drug? trafficking. SING gets infuriated and falls out with HUNG.

To pacify SING, HUNG promises to let him leave his job after the final trade with the drug-trafficker. However, SING is arrested by the police. Luckily, there is insufficient evidence against SING who resolutely refuses to help him anymore. Later, this determination is further strengthened when he learns that FONG is having his baby. To avoid FONG being victimized because of HUNG's evildoings, SING decides to help NAM to crush HUNG's gang. HUNG suspect SING of being disloyal to him and nearly kills SING.