Kurbsky's defection represents a direct political and military challenge to Ivan's rule.
The plot states that Prince Andrei Kurbsky surrendered the Russian army to the Poles and transferred his allegiance away from Czar Ivan IV.
Kurbsky becomes aligned with Sigismund against Ivan's authority.
Prince Andrei Kurbsky is said to have transferred his allegiance to King Sigismund of Poland after surrendering the Russian army.