Calculating Christmas, Chapter 1: Cinderella = x

A few weeks after The Cinderella Theorem finished, Lily's struggling to solve a problem once again involving Cinderella. When Grimm suggests she visits her friend for some field work for on the assignment, Lily happily rides out to visit her friend. But when she returns to the office, she finds a note from Calo. They are needed on a mysterious new case that starts the next day.