Newly discovered documents from the early 1920s, especially from archives in Europe and Japan, have helped the creators to piece together the backgrounds of the 13 representatives, including New China's first leader, Mao, who gathered for the first Party congress.

"We also wanted to retell the history from an international point of view. The founding of the CPC was helped by overseas communists, making it possible to conceive parallel plotlines taking place overseas," says Huang Jianxin.

Led by Vladimir Lenin, the Moscow-headquartered Communist International (1919-43) assigned Dutch communist Henk Sneevliet, who went by the pseudonym Maring, and Russian delegate Nikolsky to help Chinese people to found the CPC in 1921, according to records.

Coupled with inspiration from an unsealed archive found in Japan, the film 1921 adds espionage genre elements, exemplified by scenes featuring a Japanese spy sent to Shanghai and the two Comintern delegates escaping in a death-defying car chase.

"When we were conducting our research, we found that Japan was keeping a close eye on the communist activities in the period－it actively supported and nurtured pro-Japan forces in China," says Zheng Dasheng, a Shanghai native and co-director of 1921.

"Besides, the situation in Shanghai was quite complicated with the foreign settlements."