Spy Classroom, Vol. 3 (light novel) — Takemachi

Some Things Are Best Left in the Dark
 
After the mission to take down Corpse, Thea, Monika, Annette, and Erna have earned a break. Unfortunately, their relaxing vacation will have to wait, as they soon find themselves face-to-face with Annette's mother -- although Annette herself has no memories of her past. While the emotional reunion initially brings everyone together, it isn't long before fissures begin spreading throughout the team…