This is an episode from the Three Kingdoms. Cao cao sent a letter to Zhou Yu to summon him to surrender. Zhou Yu tore Cao's letter to pieces. Zhou Yu's classmate, Jiang Gan, was working for Cao Cao as an adviser¹, Jiang offered to travel to Wu to persuade Zhou Yu to surrender. One day while Zhou Yu was discussing with his subordinates how to defeat Cao Cao, he was told that Jiang Gan had come to see him. Zhou immediately figured out that Jiang must have come to persuade him to surrender. Zhou Yu devised a clever plan to thwart² his efforts and enlisted³ the help of his subordinate to carry it out. Then he went to meet Jiang Gan all smiles. Zhou Yu took Jiang Gan's hands and marshaled him into his tent and treated him to a banquet . When all his generals and subordinates came for dinner, Zhou Yu told those around the table: "This is an old friend or mine. Though he came from the Cao Cao camp, he did not come to persuade me to surrender. Please do not suspect him."

After the banquet, Zhou Yu pretended that he had too much and invited Jiang Gan to his bedroom for a rest. Zhou Yu soon pretended to have fallen asleep. Jiang Gan took this chance to thumb through Zhou Yu's documents. He was shocked to find a letter from Cai Mao and Zhang Yun, two generals of the Cao camp, who had written Zhou Yu to surrender. Jiang hid letter of surrender in his pocket and returned to the bed, pretending that he was sill asleep.

After midnight, someone sneaked⁴ into Zhou Yu's tent and woke him up, telling him "A messenger came from the Cao camp to say that Cai Mao and Zhang Yun were not yet a position to carry out their plan." After he heard the news, Zhou Yu went back to sleep. Jiang Gan got up again silently and snuck out of Zhou Yu's camp. He crossed the river immediately and handed the letter of surrender to Cao Cao. Cao was enraged⁵ and he had Cai Mao and Zhang Yun executed. When the news spread to Wu, Zhou Yu burst into laughter and said, "Cai Mao and Zhang Yun were the two generals I feared most. Now I fear no one." Before long, Cao cao realized that he was cheated by Zhou Yu's stratagem⁶ of sowing distrust in Cao's camp.

这个故事发生在三国时期。

赤壁大战前夕，曹操亲率百万大军，驻扎在长江北岸，意欲横渡长江，直下东吴。东吴都督周瑜也带兵与曹军隔江对峙，双方箭拔弩张，准备大战一场。

蒋干，字子翼，是曹操手下的谋士。他因自幼和周瑜同窗读书，便向曹操毛遂自荐，要过江到东吴去作说客，劝降周瑜，免得大动干戈。曹操闻知大喜，亲自置酒为蒋干送行。

这天，周瑜正在帐中议事，部下传报“故人蒋干相访”。周瑜闻讯，已经猜出蒋干来意，他眉头一皱，计上心来，连忙吩咐众将依计而行，随后带着众人亲出帐门迎接。二人相见，寒暄一番，周瑜挽着蒋干手臂同入大帐，设盛宴款待蒋干，请文武官员都来作陪。席上，周瑜解下佩剑交给太史慈，命他掌剑监酒，吩咐道：“蒋干和我是同窗契友，虽从江北到此，却不是曹操的说客，诸位不要心疑。今日宴席之上，只准共叙朋友旧交，有人提起两家战事，即席斩首！”蒋干听了，面色如土，哪敢多言！周瑜又对蒋干说道：“我自领兵以来，滴酒不饮，今日故友相会，正是：江上遇良友，军中会故知。定要喝它个一醉方休！”说罢，传令奏起军中得胜之乐，开怀畅饮。

酒至半酣，周瑜举杯祝酒道：“在座各位，都是江东豪杰，今日之会，可称作群英会！真是—同窗契友会‘群英’，江东豪杰逞威风！”随后，乘着酒兴，起身舞剑作歌：“丈夫处世兮立功名，立功名兮慰平生，慰平生兮吾将醉，吾将醉兮发狂吟。”

直喝得酩酊大醉。

宴罢，蒋干扶着周瑜回到帐中，周瑜说道：“很久没和子翼兄共寝，今夜要同榻而眠。”说着，朦朦胧胧地睡去。蒋干心中有事，想起在曹操面前曾经夸下海口，不知回去如何交代，听听外面鼓打二更，哪里还睡得着？他见周瑜鼾声如雷，便摸到桌前，拿起一叠文书偷看起来。正翻着，忽见里面有一封书信，细看却是曹操的水军都督蔡瑁、张允写给周瑜的降书。蒋干看罢，大吃一惊，慌忙把信藏在衣内。再要翻其它文书，却听周瑜梦中呓语：“子翼，我数日之内，定叫你看曹操首级！”蒋干口中含糊答应着，连忙吹了灯，匆匆睡下。

清晨，有人入帐叫醒周瑜，说道：“江北有人来……”周瑜急忙止住他，看看蒋干，蒋干只装熟睡。周瑜和那人轻轻走出帐外，又听那人低声说道：“蔡瑁、张允说，现在还不能下手……”声音越来越低。蒋干心中着急，可又不敢乱动。不一会儿，周瑜回来躺下睡了。蒋干怕惊动周瑜，等周瑜睡熟，偷偷地爬起来，径直走出军营，守营军士也不阻拦。他来到江边，寻着小船，飞一般驰过长江，回见曹操。

其实，这一切都是周瑜定下的反间计。他知道曹军中只有蔡、张二将精通水战，便设下此计，想借曹操之手杀掉这两个人。曹操果真上了当，斩了蔡瑁、张允。等到众人蔡瑁,张允的头送上时,曹操才省悟过来，已经晚了，只好另换了两个水军都督。结果，赤壁一战，曹操水军一败涂地。