A man is found dead at the base of a mountain peak. Was it a suicide? Could it be murder? With the deceased's wife as the prime potential suspect, the investigator in charge of the case begins to tumble down a rabbit hole of obsession as he investigates her.
The thing that makes Park Chan-wook's films so special, for me at least, is while other films employ dream sequences, or visions, or flashbacks, no other filmmaker uses them in a story without feeling a separation between real and unreal. Using picture and sound, he somehow harnesses the subconscious in a visceral way.
Comparisons to Alfred Hitchcock's Vertigo provide a good frame of reference. This too is a story of murder, obsession, love...but this is far better.