From the back cover:
DISCOVER WHAT FOUL CREATURE HUNTS FOR NEZUMI BLOOD IN THE SHADOWLANDS
As a band of samurai travels through the dangerous, twisting landscape of the Shadowlands they encounter strange rat-like creatures called nezumi. The scouts describe a monster who hunts their tribe and they plead with the samurai for aid. Faced with a possible lead on their adventure, the samurai must choose whether they will help or destroy the scouts of the Knotted Tails tribe.
A supplemental storyline for Mask of the Oni, The Knotted Tails expands upon the information presented in Shadowlands, a sourcebook on the twisted machinations of the fallen Kami Fu Leng and introduces players to a remorseful tribe of nezumi. This storyline for the Legend of the Five Rings Roleplaying Game offers heroes a mystery to solve and a slight reprieve from the the dangers of the Shadowlands while they journey onward towards Shiro Hiruma.
This is an optional bonus storyline that may be played within Mask of the Oni, an adventure for the Legend of the Five Rings Roleplaying Game. Encounters are designed for a party of four PCs of rank 2, though these can be adjusted for parties of any size and ranks by using Gauging an Encounter on page 310 of the core rulebook.