Several months have passed since the Jewel Seed incident, and Nanoha Takamachi is getting ready to welcome Fate Testarossa back from her trial with the Administrative Bureau. Having received conditional clemency for her role in preventing the crisis, Fate has been allowed to attend school with Nanoha. However, before the two girls can settle into their daily lives together, a group of dark mages suddenly descend upon them. Overpowered by their unknown assailants, Nanoha and Fate have their mana absorbed by an ominous grimoire, and both Raising Heart and Bardiche are damaged in the process.