Retired black knight Lina and her husband Joshua have relocated to the idyllic eastern region—for Lina to recuperate from her old injuries, and Joshua to work and study in hope of becoming the next prime minister. With renewed passion for one another, the two are happy to get the chance to live in peace together...but their tranquility doesn't last long!

A ghastly illness with connections to Lina's past has broken out in the neighboring region. Desperate to find a cure for the sick and to prevent the disease from spreading further in the poverty-stricken territory, Lina and Joshua travel to the small village of Riberry to get to the bottom of the mystery.

However, the puzzles don't end there. Why have a literally washed-up black knight and a half-drowned girl appeared in Riberry? And just who is this woman who keeps calling on Joshua and sending him letters? Doesn't she know he's married?!