The Holy Grail of Eris, Vol. 5 (manga)

Having survived the Silent Ladies' Tea Party with the help of Scarlett and Abigail, Constance must now prepare for her meeting with Cecilia-the sly, deceitful princess. She hopes it'll be a chance to learn more about the incident ten years ago... but when Connie arrives at the palace, the mystery only deepens as a member of the royal family goes missing. All clues point to one suspicious Solditan merchant, but if Connie wishes to track him down, she'll need to face even greater dangers lurking in the shadows...