I figured out what you call "spoiling" at the thirty-seven minute mark when Nishi was in an office with "dead" Wada. Also, Nishi's words at the volcano? By my reckoning that's under one-third of the way into the film. We already knew a man had committed suicide, and that Nishi's motives for marriage were dubious. The cake? Hello? The first scene pretty much set the plot and needed clues through the reporters' banter. Golly. Oh, and I saw this film before IMDB was created. Then too, some of the Japanese historical literature I'd read extoll mandatory suicide, at the behest of "masters", as regular fare, so I had a little insight. Vengeance too is part the Samurai tradition. In summation, all the pointers were there within forty-five minutes at Wada's funeral when Nishi recruited Wada, asking him if he did not want revenge. A classic Samurai tale in a modern setting, in the making.
All that said, I knew what to expect upon my first visit to South Island, New Zealand, but nothing was ruined by either my viewing of hundreds of pictures, or a dozen films and amateur videos. My point being that Kurosawa's art is in it's exposition, while plotting is merely framing of the canvas. It's what's inside the frame that matters. Just my opinion, nothing more or less.