They managed to persuade the dying emperor to appoint Cao Shuang (with whom they were friendly) and Sima Yi (who was then with his troops at Ji County (汲縣; in present-day Xinxiang, Henan) as the regents instead.
In 243, Sima Yi's position was further strengthened by another successful deployment: Zhuge Ke, a general of Wei's rival state, Eastern Wu, was constantly sending agents to Shouchun (壽春; around present-day Shou County, Anhui) to prepare an invasion, so Sima Yi led Wei forces to Shu County (舒縣), Lujiang Commandery (盧江郡) near the Wei–Wu border.
Upon hearing the news, the Wu emperor Sun Quan immediately ordered Zhuge Ke to withdraw to Chaisang (柴桑), Yuzhang Commandery (豫章郡).
Sima Yi's popularity and influence instantly multiplied as he was cheered as being able to scare away the enemy numbering over 100,000 without a fight and thus secured the border and saved Shouchun from certain attack.
[4] However, two months later, he lost to Shu forces led by Wang Ping and Fei Yi at the Battle of Xingshi and barely escaped back to Chang'an.
Potentially to deceive Cao Shuang into letting down his guard, Sima Yi stopped engaging in any political activity in May 247 and retired on the grounds of illness.
In the same year, Cao Shuang followed the advice of Li Sheng, Deng Yang and Ding Mi in order to maintain his power.
Sima Yi then went to see Empress Dowager Guo and coerce her into issuing an imperial order for the arrest of Cao Shuang and his brothers under charges of treason.