Chi Mo Sai (Yuen Wah) meets Wong (Roger Kwok) in Auntie Fei's (Yuen Qiu) cafe and learns that Wong has photographic memory. He decides to exploit this skill by teaching Wong how to play Mahjong, but Fei, Wong's boss, strongly objects to it. Despite Fei's objections, Wong learns Mahjong from compulsive gambler Chi Mo Sai. He impresses triad boss Tin Kau Ko (Wong Jing). Wong falls in love with Tin's mistress (Theresa Fu) and is beaten by Tin's men. Wong then becomes crazy. Luckily, Fei cured him using Mahjong. Fei wanted Wong to beat Tin in the "King of Mahjong" competition and be the King of Mahjong. The film ends with a climactic "King of Mahjong" Competition. It is the only film made in 2005 to boast of having a sequel made in 2005.

In the wake of his father's heart attack, Ken must battle his father's mistress - who persuaded her lover to transfer the grand master title to her in the event of his death - for the rightful claim to the family fortune in a riveting game of mahjong.