In feudal Japan, samurai warriors Washizu and Miki come across a mysterious spirit in the forest who prophesizes their futures. The spirit predicts that Washizu will become the lord of Spider's Web Castle while Miki's descendants will eventually rule. Skeptical yet tempted, Washizu confides in his ambitious wife, Asaji, who convinces him to take drastic measures to fulfill the prophecy. Encouraged by his wife's ruthless ambition, Washizu embarks on a path of treachery beginning with the murder of Lord Tsuzuki, assuming control of Spider's Web Castle.

As Washizu attempts to solidify his grip on power, paranoia and instability seep into his reign. Asaji goads him to commit further atrocities to ward off potential threats, deepening his descent into madness. Meanwhile, the seeds of suspicion grow among the ranks, as Miki and others begin to question Washizu's right to the throne. Amidst a backdrop of political intrigue and supernatural elements, Washizu's actions lead the forces against him to converge, pushing the tale towards a dire and inevitable climax.