Episode 4 recap: A student has revealed the identity of Ye Xuan Min.

Zeng Ji Wu came to the dance hall to arrest Lou Ming Yuan. Lou Ming Yuan confessed everything, telling Ou Xiao An to take the Falling Cherry Blossom plan away from Shanghai, and to change the neon lights at the dance hall entrance to indicate that it is unsafe. Lou Ming Yuan told Ou Xiao An the secret code, knowing that someone would come to help him.

Zeng Ji Wu suspected that Ou Xiao An, who frequently visits the dance hall, is a Communist spy. When the incident happened at the dance hall, Li Shao Tang, seeing the changed neon lights, got scared and quickly left. Ou Xiao An went back and burned the Falling Cherry Blossom plan.

When Zeng Ji Wu knocked on the door, Ou Xiao An covered up the smell of burned paper by stir-frying. He was then told by the Colonel to go interrogate the prisoner he had just arrested.

At the interrogation room, Ou Xiao An saw Lou Ming Yuan badly beaten. The Colonel pretended to question him, suspecting he had inside connections with Shi Gao Ta. The Japanese troops continued to torture Lou Ming Yuan. Ou Xiao An, unable to watch, questioned him directly. Lou Ming Yuan intentionally implicated Ou Xiao An, trying to provoke him to kill him.

Remembering their past battles together, Ou Xiao An raised his gun at Lou Ming Yuan, but the Colonel stopped him. The Colonel had the doctor inject Lou Ming Yuan with a truth serum. Lou Ming Yuan resisted with willpower, so the doctor increased the dosage.

Enduring the drug's torment, Lou Ming Yuan defiantly sang the March of the Volunteers, angering the Colonel. Meanwhile, Qin Mo Qing, disguised as a man, went to the cheongsam shop. Wang Qiu Shui told her to have a clear conviction, control her reactions, and not let the enemy read her body language. He also said the organization is considering her party membership application.

Qin Mo Qing was worried that her brother going to Chongqing would affect the organization's assessment of her. Although both the Japanese and the Nationalist secret police are targeting them, Wang Qiu Shui said they will follow the organization's arrangements, even though they lack resources to move the supplies. Qin Mo Qing realized they need travel passes and said she has a solution.

Zeng Ji Wu captured the students Liao Shu Yun and Zheng Bang Yao. Zheng Bang Yao, fearing for his life, revealed Ye Xuan Min's appearance. The students took to the streets in protest, demanding the Japanese military release the students. Wang Qiu Shui was worried this was a Japanese military plot and wanted to persuade Ye Xuan Min. Ye Xuan Min couldn't bear to see the students suffer and decided to show himself to help the students find a way to talk to the puppet government.

The Japanese military surrounded them, and the students huddled together to protect Ye Xuan Min. Zeng Ji Wu sent people to violently suppress them, and they took Ye Xuan Min away. The Big Bridge criticized Zeng Ji Wu for arresting someone in front of the reporters, worried it would ruin his plan, and had Ou Xiao An go interrogate Ye Xuan Min.

Ye Xuan Min demanded the Japanese release the students, and the Japanese required him to appear in front of the reporters to explain. The Japanese released Ye Xuan Min in front of the reporters, then had Zeng Ji Wu re-arrest him. Qin Mo Qing learned that Zheng Bang Yao had betrayed Ye Xuan Min, and felt it was because of his own actions that Ye Xuan Min's identity was exposed.

The Big Bridge had Ye Xuan Min brought back to the interrogation room, questioning him about when he came to Shanghai and showing him a photo of Lou Ming Yuan. Ye Xuan Min remained unfazed, so the Big Bridge brought out a photo of Ou Xiao An. Ou Xiao An, following Lou Ming Yuan's instructions before his capture, went to the alley to find the contact person Li Shao Tang.

The two gave each other the secret code, and Li Shao Tang already knew the Big Bridge was trying to capture him. He was panicked and didn't know what to do, claiming he was just a normal biochemist. Ou Xiao An suspected he had been discovered by the Japanese at the dance hall, and told him to leave Shanghai first. Li Shao Tang felt the Falling Sakura plan had been burned, and Ou Xiao An said he would provide the handwritten notes for him.

They first arranged for him to stay somewhere, then told him to find Qian San. Li Shao Tang asked Ou Xiao An's name, but Ou Xiao An told him to just focus on his own matters, there was no need for them to know each other. The time moved back to 1945, and Li Shao Tang retrieved the 1941 materials to re-examine the files on Lou Ming Yuan and Ou Xiao An.