The upcoming mystery thriller “The Owl” added imagination to a record in the Annals of Joseon Dynasty about Crown Prince Sohyeon’s suspicious death.

“Our film started from day blindness. I started with the idea of a protagonist with day blindness getting to witness something,” director An Tae-jin said during a press conference held at CGV Yongsan on Thursday. Day blindness is an inability to see as distinctly in bright light as in dim light.

As the director developed his idea into a movie script, he came across a record about the death of Crown Prince Sohyeon, the first son of King Injo of the Joseon Dynasty (1392–1910), which stated he died as if poisoned to death, without any details.

"Nobody knows what really happened. I just tried to make sure we stick to the historical fact that King Injo did not like Crown Prince Sohyeon’s family. I made sure I didn’t change that and then added my imagination," the director said as he explained what he considered when further developing the story for the movie.

In the film, Kyeong-Soo (Ryu Jun-yeol) is a day-blind acupuncturist in the palace. He is unable to see anything during the daytime, but, strangely, he can see like a normal person at night. One evening, Kyeong-Soo happens to witness the death of Crown Prince Sohyeon. This death leads King Injo (Yoo Hae-jin) into madness. Kyeong-soo, who is used to keeping secrets, considers revealing the truth behind the crown prince’s death.

According to the director, "The Owl" has two big pillars in its story.

"One is the protagonist witnessing something accidentally leading to his involvement in an unexpected and troubling situation. The other is stories about a historic figure that blends into the film with my imaginary details. I tried to balance these two pillars," An explained.

The director also talked about the message he wants to convey through "The Owl."

“The film’s key message lies in (Kyeong-soo) witnessing something. I hope that the audience can watch the film and think about what decision they would make when they get to witness the truth regardless of its size,” he said.

During the press conference, Ryu and Yoo shared how they prepared to play their respective characters. Even though they showed synergies in the previous two movies they worked together -- “A Taxi Driver (2017)" and “The Battle: Roar to Victory (2019)," the way they prepared for the characters was quite different.

“I’ve talked to people with day blindness and tried to look into their daily life,” Ryu said.

The actor added that although they could not see anything under the light, it seemed like they are looking at something. To him, it felt like they are looking at a certain path that they are hoping to pursue.

“I talked with the director about whether I should close my eyes when performing blind Kyeong-soo. It could have been easier that way,” Ryu said. “But I wanted to show the dreamy look that I saw in those people's eyes.”

On the other hand, Yoo, who played King Injo afflicted with facial nerve paralysis, did little research before shooting the movie.

"I just thought of how I can effectively portray this character. I tried to focus. I think if you actually become the character you don’t have to prepare for details separately. It just comes naturally. It is something that I have learned through practicing for theater performances," Yoo said.

Towards the end of the press conference, Ryu said he learned a lot working with Yoo for the third time.

“I learned his know-how and realized why he is such a beloved actor. I was moved by his performance,” Ryu said.

“It is our third project together and on the set, I could see that Jun-yeol is becoming a big actor. I think he is a bit shy and humble to talk about his own improvement but it was visible that he has become a big actor,” Yoo complimented.

After hearing Yoo’s compliment, Ryu dropped his head and teared up slightly.

The film will hit local theaters on Nov. 23.