In April or May 248, Zhang Dang (), a palace eunuch, illegally transferred 11 women out of the imperial harem and presented them to Cao Shuang to be his concubines. Cao Shuang and his close aides thought that Sima Yi was seriously ill and could no longer do anything, so they plotted with Zhang Dang to overthrow the emperor, Cao Fang, and put Cao Shuang on the throne. However, they were still wary of Sima Yi and did not lower their guard against him.