Singapore, the present day. Mai Wei (Mark Lee), a successful branch manager for slimming company Natural Beauty, is sacked for cutting corners in the name of profit and attracting the ire of customers. Enraged, he sets up a rival company, My Way Slimming Centre, with several Natural Beauty employees, including Jie (Jeremy Chan), younger brother of his wife Zu Er (Yeo Yann Yann). As Natural Beauty continues to expand, Mai Wei goes on the offensive, licensing a herbal slimming pill, Dadavianxiaovoo, that contains a banned substance. As his company's image representative he chooses the massively overweight Wang Yao Yao (Tay Yin Yin), daughter of his favourite wonton noodle stall owner (Wang Lei), and feeds her the pills in large doses. Meanwhile, Zu Er, who's desperate to have a child after eight years of marriage, starts believing the gods have cursed them because of her husband's unscrupulous business practices.

King of Mahjong centres on the decade-long feud and eventual reunion of Wong Tin Ba and Ah Fatt. 20 years later, Wong Tin Ba, who is now a world-acclaimed mahjong champion and magnate, shows up in Ipoh to challenge Fatt to a final showdown – The World Mahjong Championship. Despite Wong’s insistence, Fatt declines to join the competition as he is determined and contented to lead the life of a commoner. In a bid to force Fatt into the showdown, Wong abducts Fatt’s wife, Ramona, and threatens her to be on his alliance. Fatt has no choice but to join the championship as Wong holds his wife hostage. On the mahjong table, Fatt and Wong compete as the finalists; Master Ru’s secret legendary mahjong move and the truth comes to light as the winner emerges...