唐朝女皇武則天，為了鎮壓反對她的人，任用了一批酷吏。其中兩個最為狠毒，一個叫周興，一個叫來俊臣。他們利用誣陷、控告和慘無人道的刑法，殺害了許多正直的文武官吏和平民百姓。
有一回，一封告密信送到武則天手裡，內容竟是告發周興與人聯絡謀反。武則天大怒，責令來俊臣嚴查此事。來俊臣，心裡直犯嘀咕，他想，周興是個狡猾奸詐之徒，僅憑一封告密信，是無法讓他說實話的；可萬一查不出結果，太后怪罪下來，我來俊臣也擔待不起呀。這可怎么辦呢？苦苦思索半天，終於想出一條妙計。
他準備了一桌豐盛的酒席，把周興請到自己家裡。兩個人你勸我喝，邊喝邊聊。酒過三巡，來俊臣嘆口氣說：“兄弟我平日辦案，常遇到一些犯人死不認罪，不知老兄有何辦法？”周興得意地說：“這還不好辦！”說著端起酒杯抿了一口。來俊臣立刻裝出很懇切的樣子說：“喔，請快快指教。”周興陰笑著說：“你找一個大瓮，四周用炭火烤熱，再讓犯人進到瓮里，你找一個大瓮，四周用炭火烤熱，再讓犯人進到瓮里，你想想，還有什麼犯人不招供呢？”來俊臣連連點頭稱是，隨即命人抬來一口大瓮，按周興說的那樣，在四周點上炭火，然後回頭對周興說：“宮裡有人密告你謀反，上邊命我嚴查。對不起，現在就請老兄自己鑽進瓮里吧。”周興一聽，手裡的酒杯啪噠掉在地上，跟著又撲通一聲跪倒在地，連連磕頭說：“我有罪，我有罪，我招供。”
故事見於《資治通鑑·唐則天皇后天授二年》。成語“請君入甕”，比喻用某人整治他自己。
kindly step into the vat--try what you have devised against othersin order to suppress those who were against her, wu zetian, the empress of the tang dynasty (618-907), appointed a few merciless persons to be judges. two of them were extremely brutal; one was called zhou xing and the other was called lai junchen. they killed many upright civil and military officials as well as ordinary people by framing up cases against tham and by administering inhuman corporal punishment to them.
once, wu zetian received a letter which informed against zhou xing. the letter aside that zhou xing was plotting a rebellion in collaboration with others. wu zetian was furiously angry when she read the letter, and immediately ordered lai junchen to deal with the case severely. hearing the order, lai junchen had misgivings about it. he knew that zhou xing could not be forced to tell the truth merely by using a letter informing against him because he was very sly and crafty. lai junchen also knew that he would not be for given if he should fail in dealing with the case, because the empress would certainly blame him and punish him. how could he solve the problem then? he turned the problem over and over in his mind, and finally thought out a "brilliant scheme".
lai junchen had a sumptuous feast prepared, and invited zhou xing to his home. the two of them urged each other to drink, and they talked while drinking. after the wine had gone round three times, lai junchen pretended to sigh, "when ihandle cases in ordinary times, i often com across prisoners who stubbournly refuse to admit they are guilty. i wonder if you have any effetive measures." hearing this, he took a sip of the wine. lai junchen immediately pretended to be very earnest, saying, "oh, please do tell me at once." smiling insidiously, zhou xing said, "get a big vat, scorch it hot with charcoal fire all around, and then let the prisoner come into the vat. will the prisoner fail to make a confession of his crime?" hearing this. laijunchen nodded his head in approval repeatedly. he then ordered his subordinates to bring a big vat, and had a charcoal fire lit all around it as zhou xing had said. he then turned to zhou xing and said, "someone in the imperial court has informed against you, saying that you are plotting a rebellion. the empress has ordered me to deal with the case severely. so i beg your pardon, but would you kindly step into the "someone in the imperial court has informed against you, saying that you are plotting a rebellion. the empress has ordered me to deal with the case severely. so i beg your pardon, but would you kindly step into the vat?" hearing this, zhou xing dropped his wine cup to the ground and the cup broke with a crash. then he knelt down with a flop, nodded repeatedly and said, "i am guilty. i confess i am guilty."
this story appears in a general history as a mirror of past events by sima guang of the song dynasty. from this story, people have derived the set phrase "kindly step into the vat -- try what you have devised against others".