Mu Lan (Chan Miu Ying)'s father, Fa Wu (Lo Ka Ying) was framed up by the Long's father and son when Wu accidentally discovered their evidence of crime. The Fa's family was then on the list of military troop to fight against the barbarians. Mu Dai (Wai Ka Hung) is weak and Lan also did not wanted his father to be recruited in the troop. Lan then decided to disguise herself as a man to join the army. 

 Lan and Ho Ko Sing (Wong Hei) was an odd couple and teased each other in the military camp. Sing later found out Lan was a girl so he helped Lan whenever she was at risk. Lan was not aware of Sing's assistance. Meanwhile, The Long's sent spies to get Lan into trouble. Lan, however, overcame the danger and was even awarded by the royal court and got promoted. The Emperor even bestowed upon Lan to marry his own sister, Long Siu Siu (Fu Ming Hin) ...