Yun Fei Yang is the viciously bullied orphan who takes on the unpleasant tasks at a formidable kung-fu school. Constantly mocked by the other students of the school, Yun counts as his only friend the daughter of the resident master. Any internal wrangling between the various members is put to one side when a swordsman from a rival clan reminds the master of the duel he must take part in once a decade. Unfortunately the defending clan chief is well aware that his rival is more powerful than himself. The expected defeat is further complicated when a wandering swordsman arrives on the scene and joins himself to the injured party, immediately adding to Yun's woes. The ensuing series of confrontations and intrigues soon reveals the individual motives that the numerous parties all have and the role they play in the fate of the martial world. After finally understanding his own past and upbringing, Yun is ready to take on the mantle of avenger for his school and win back the respect that his colleagues have lost. With fighting skills that had been taught to him by a shrouded figure, Yun steps out of the shadows and reveals himself to be anything but the harassed orphan that everyone enjoys picking on. However to have any kind of hope against his nearly superhuman foes, the young fighter must uncover the secrets of his clan's 'Silkworm Technique' and transform himself completely.

故事敘述武當雜役雲飛揚為掌門青松之私生子，因身世不明而飽受同門欺凌，雖受其父夜授武功，但卻被警告所習得之武功絕不可在人前顯露。武當與無敵門相互敵對，兩派十年一戰，青松接連慘敗，更在雙方第三次對決中，險喪生於無敵門門主獨孤無敵滅絕魔功之下。然則獨孤無敵忌於青松師兄燕沖天所修習之天蠶神功，逐與青松訂下兩年不戰之約，閉關修煉滅絕神功第九重。

豈知此空檔中，武當派昔年仇敵逍遙谷碧落賦中人亦悄悄滲入武當。逍遙谷少谷主傅玉書於青松負傷之時使計獲得其信任，並蒙收錄門下。逍遙谷眾人先是伺機刺殺青松，並嫁禍於雲飛揚；後則殺害具威望之弟子，終使傅玉書成功坐上武當掌門之位。雲飛揚依青松遺命前往無敵門尋獨孤無敵之妻沈曼君，方得知自己身世，卻不幸遭獨孤無敵所傷，幸得沈曼君母女所助，始得倖免。

傅玉書奪得武當掌門之位後為重振碧落賦之名，排除異己，用計殺害燕沖天，並且大肆誅殺武當眾弟子。雲飛揚自同門女弟子倫婉兒口中得知一切皆乃傅玉書所為，合眾人之力成功習得於沈曼君處取得之天蠶神功，終擊敗碧落賦眾人，清理門戶，為父報仇。