周瑜打黃蓋

fig. with the connivance of both sides; fig. by mutual consent; cf Wu patriot Huang Gai submits to mock beating at the hands of General Zhou Yu to deceive Cao Cao 曹操[Cao2 Cao1] before the 208 battle of Redcliff 赤壁之戰|赤壁之战[Chi4 bi4 zhi1 Zhan4]