had entered Tang territory and put Wucheng (乌城, in modern Yulin, Shaanxi) under siege.РLi Shimin, fearful that Li Jiancheng and Li Yuanji would use this opportunity to act against him, decided to act, particularly at the urging of his brother-in-law Zhangsun Wuji(长孙无忌) and ? Yuchi Jingde(尉迟敬德).РHe had Fang Xuanling(房玄龄) and Du Ruhui(杜如晦) secretly recalled to his mansion(宅邸) to draw the plans for action, and then one night submitted(递交) a secret accusation to Emperor Gaozu(唐高祖), accusing Li Jiancheng and Li Yuanji of affairs with Emperor Gaozu's concubines(妃子) and plans to kill him.РEmperor Gaozu was surprised by the accusation and promised to handle Li Shimin's accusation the next day, and summoned the high level officers Pei Ji, Xiao Yu, and Chen Shuda to prepare to act on the accusations