A Step into the Past

Hong Siu-lung is a 21st-century VIPPU special agent in Hong Kong. In the first episode, Hong and his colleagues stand guard at an exhibition of the First Emperor's Terracotta Army. One of Hong's colleagues notices that one of the terracotta warriors bears a striking resemblance to Hong. Moments later, wealthy businessman Lee Siu-chiu is attacked and held hostage at the museum by a madman who had suffered losses in the stock market. Hong rescues Lee and defuses the crisis.

Hong is unhappy despite his success in his career. He has just broken up with his girlfriend, Chun Ching, after a seven-year-long relationship. She insisted that they wed but he preferred to continue their relationship without a proper marriage. Chun married another man and Hong becomes depressed.

Impressed with Hong's rescue attempt, Lee Siu-chiu and Doctor Wu Yau recruit him for a secret time-travelling experiment. Hong agrees to help them in exchange for an opportunity to travel back in time to salvage his failed relationship with Chun Ching. He is tasked to travel back more than two thousand years to the Qin dynasty, half an hour prior to the coronation of Ying Ching in 247 BC, and document the event with a digital camera before a swift departure. However, a critical error occurs during the traveling stage and Hong is sent further back in time three years earlier than originally planned. He is now trapped in the Zhao state of the Warring States period in 250 BC.

In order to return to the future, Hong has to make an arduous journey across thousands of miles in ancient China to activate a device at a specific location and time. He was warned that making even a slight change in the grand scheme of events will trigger a chain reaction of catastrophes that will alter history.

Hong enjoys a series of adventures in history. His knowledge of the 21st century, intelligence and experience as an elite special agent, as well as his prowess in martial arts, enables him to make a strong stand in history. He enters the service of various lords and nobles, and becomes a valuable ally to them. Concurrently, he becomes involved in romantic relationships with four women. The first, Sin-yau, is a wandering female assassin and the first person he meets after travelling back in time. The second, Wu Ting-fong, is the beautiful but spoiled daughter of a wealthy noble. The third is a pretty female scholar named Kam Ching, who resembles his 21st century girlfriend Chun Ching in appearance and shares a similar name (completely homophonic in Standard Mandarin). The last is Princess Chiu Sin, the daughter of the king of Zhao, who dies in a tragic incident later. He also befriends the king's sister Chiu Nga and her son Chiu Poon. Meanwhile, he foils the evil plans of Chiu Muk, a secret agent from the Chu state, and becomes Chiu's enemy. Chiu Muk's henchman Lin Chun also sees Hong as his greatest rival.

Ying sees Hong as a valuable ally in his future endeavors and wants to retain him as an adviser. However, Hong begins to feel regret when he sees the evil creation of his efforts, fulfilling the predestination paradox. He is aware that he is not destined to leave his mark in history and refuses to stay in the imperial court. He leaves with Wu Ting-Fong and Kam Ching, who are both happily married to him at last. Ying sends his troops to pursue Hong and eventually decides to exile Hong and decrees that the name "Hong Siu-lung" shall henceforth be purged from history. All books and historical records pertaining to Hong are ordered to be destroyed, which leads to Chun Chi Wong's notorious practice of the burning of books and burying of scholars.

Hong and his family find paradise in the plains far from the urban regions. Hong and Wu Ting-Fong have a son. In the final moments of the last episode, Hong's son tells him he wants to change his name from Bowie to Hong Yu, a man who historically become a prominent military general who overthrew the Qin dynasty that has a tragic end due he became a dictator. Hong then exclaims in English "Shit!"

• Louis Koo as Hong Siu-lung (Chinese: 項少龍; pinyin: Xiàng Shàolóng), the protagonist of the story. Born in 1975, Hong was orphaned at the age of three and spent most of his childhood in foster care. Sociable, diligent and smart, Hong graduates to VIPPU officer after only one year of training. When his girlfriend of seven years breaks up with him, Hong agrees on a time travelling project organised by Lee Siu-chiu on the condition that he will see his girlfriend again when he returns.
• Raymond Lam as Chiu Poon / Ying Ching (Chinese: 趙盤 / 嬴政; pinyin: Zhào Pán / Yíng Zhèng), the son of Princess Chiu Nga. He is despised by other nobles due to his mother's promiscuous reputation. After Hong rescues Lady Chu from the Zhao state, Chu mistakes Chiu as her deceased son, Ying Ching. Through Hong's coercion, also compounded by his personal lust for power and vengeance, Chiu becomes the crown prince of Qin and ascends to the throne, subsequently becoming the First Qin Emperor, the First Emperor of a unified China.
• Kwong Wa as Lin Chun / Lo Oi (Chinese: 連晉 / 嫪毐; pinyin: Lián Jìn / Lào Ǎi), a swordsman who used to serve Chiu Muk. He is abandoned by Chiu after Hong injures his right arm in a duel. During his banishment, Lin meets Lo Oi, a left-handed swordsman. After convincing Lo to teach him left-handed swordplay, he kills Lo and takes his identity.
• Sonija Kwok as Chun Ching / Kam Ching (Chinese: 秦青 / 琴清; pinyin: Qín Qīng / Qín Qīng). Chun Ching was Hong's girlfriend of seven years, but broke up with him after he reneges the wedding promise. Hong agrees to participate in a time-travelling project after he was assured that Chun Ching would return to him. After Hong is transported to two thousand years back, he meets Kam Ching, a female scholar who resembles Chun Ching in appearance and they develop a romantic relationship.
• Jessica Hsuan as Wu Ting-fong (Chinese: 烏廷芳; pinyin: Wū Tíngfāng), the impulsive and spoiled daughter of the Qin loyalist Wu Ying-yuen. Although disgusted by Hong's flirtatious nature, she gradually becomes jealous of her own accord when she sees him with other maidens. Nonetheless, Wu develops a close friendship with Princess Chiu Sin and often visits her.
• Joyce Tang as Sin-yau (Chinese: 善柔; pinyin: Shànróu), a female assassin. She was an orphan. She becomes the apprentice of Mohist practitioner Cho Chau-to, also becoming an assassin who kills people for money. She is the first person Hong meets after he is transported back in time.
• Michelle Saram as Princess Chiu Sin (Chinese: 趙倩; pinyin: Zhào Qiàn), the daughter of King Hao-sing of Zhao. She develops feelings for Hong after he "rescues" her from the palace. She is also Hong's first love after he returns in time.
• Waise Lee as Chiu Muk (Chinese: 趙穆; pinyin: Zhào Mù), a secret agent who works for the Chu state as a spy in Zhao.
• Shirley Yim as Chiu Nga (Chinese: 趙雅; pinyin: Zhào Yǎ), the younger sister of the king of Zhao. She is Chiu Poon's mother and a close friend of Hong Siu-lung.