What is the main plot of the Campaigns in Heroes V?

It all begins with the wedding of King Nicholas of the sacred Griffin Empire and Lady Isabelle. However, the wedding is interrupted by a demon who invades right in the middle of the ceremony. This can only mean one thing – a new invasion from Shio*. While Nicholas leads the main forces of the empire into battle, Isabelle leads her own rebel war, helping her beloved. This war will be remembered in the history of Ashan* as the "War of Queen Isabelle." In the final battle, Nicholas is mortally wounded by a certain Agrail, one of the close associates of the demon lord, Kha-Beleth. The king dies in the arms of his uncle Godric, making him swear that Isabelle will rule the country. Isabelle, in turn, makes a vow to