What is the plot of "The Assassins"?

‌What is the plot of "The Assassins"?
I haven't seen the movie and I wasn't really paying attention, but there is so much talk about it that I'm curious.
Does it imply that President Park Chung-hee was behind the incident involving the shooting of First Lady Yuk Young-soo?
Is that why it's causing such a stir?