It has been several months since the Jewel Seed crisis, and Nanoha Takamachi prepares to welcome back Fate Testarossa after her trial with the Administrative Bureau. Despite receiving a conditional pardon for her role in preventing the catastrophe, Fate is now allowed to attend school with Nanoha. However, as they begin to settle into their routine, a group of dark mages abruptly attacks them. Nanoha and Fate are overpowered by these mysterious assailants, who absorb all their mana and damage their weapons, Raising Heart and Bardiche. The culprits of this sudden ambush are the Wolkenritter: a quartet consisting of Vita, Signum, Shamal, and Zafila, who were summoned by the Book of Darkness to execute its evil plan. The book is currently in the possession of Hayate Yagami, an innocent young girl who is unaware of its true nature. The Wolkenritter, using the mana they stole, are duty-bound to complete the book at any cost. With their weapons broken and mana depleted, Nanoha and Fate must act fast to regain their power and confront the Wolkenritter before they complete the Book of Darkness. Failure to do so will result in the unleashing of its catastrophic magic upon the world.