Secrets of the Silent Witch, Vol. 4.5 -after-: Casebook of the Silent Witch

The school festival may be over, but a series of mysterious happenings around the academy promises to keep Monica and the rest of the student council busy. As winter break approaches, food begins to disappear, a lost girl turns up at school, students start seeing ghostly balls of fire, and the second prince becomes the target of a dubious charm. Whether the trouble is big or small, Detective Monica and her mystery novel–obsessed familiar, Nero, will get to the bottom of it with help from their friends and a little unchanted magecraft!

[From Yen Press]