1933年，喜峰口长城战役，中方二十九军以民间大刀对抗日军刺刀，大获全胜，点燃民族抗战信心，以此扬名万里。故事围绕时代动荡中，“长城大刀”发明权的争夺展开，江湖各路奇人义士一一粉墨登场，其中有洒脱豪爽的军官妻子阚智慧（许晴饰），刚正守义的侠客孔鼎义（张傲月饰），娇艳欲滴的少女青青（春夏饰），黑白难辨的真假军官沈飞雪（李光洁饰/黄觉饰），以及色欲熏心的疯汉二堡（耿乐饰）等，描绘出一幅快意恩仇、活色生香的民国武林画卷。道义与情感的裹挟，荣誉与生存的困境，身处江湖的每一个人，都必须在其中做出自己的选择。

The widow of a famed general teams up with an impostor posing as her late husband and schemes to steal the secrets of an elderly master swordsman. Their plans are complicated by the master's grandson, who is himself torn between his filial duty and the affections of his adopted sister.