As can be seen from the two empty bowls in the kitchen, the two people who sent sobering soup to Dai Zhanyuan and Teng Wu's room should have sent the empty bowls back to the kitchen. From Lu Yongmin's point of view, it is proved that Su Manyun sent Dai Zhanyuan a hangover cure soup, and Du Zilong and why can know that Ruan Ruyu sent Wu Teng a hangover cure soup, so it was Su Manyun and Ruan Ruyu who went to the kitchen after Du Zilong.

Su Manyun was cracking the code with Gu Hetong at the time of the crime. After breaking the code, he tried to negotiate with the doorman to send the document out, but it didn't work. Su Manyun can be ruled out from the testimony of the doorman. Ruan Ruyu was the last person to leave, and it is basically inferred that the murderer was Ruan Ruyu.

The real purpose of Wu Teng's banquet.

From the clues, we can know that someone stole the document before and was arrested immediately. Wu Teng's secret message clue shows that the person who stole the document died and intercepted a letter to the wasp. The Japanese side suspected that the code-named "Wasp" had infiltrated our army, and demanded that Wu Teng strictly investigate and put you in the urn. Therefore, the real purpose of Teng Wu's banquet is to steal documents. Teng Wu made a fake document to lure the wasp out.

There are strange symbols in the photos in the secret letter. Gu Hetong and Su Manyun independently investigated the photos and found that "Shanxi-Chaji" was different from the location "Hubei-Henan-Anhui" in the previously translated documents, so Teng Wu made a fake document to lure the wasp out of the hole.