Mr. Mouse was a mouse which has been trained by Oboro to become a valuable helper in his investigative work. Indeed, Mr. Mouse was able to follow suspicious people without getting unwanted notice, and look for clues in the tiniest places. One instance where Mr. Mouse's work became crucial, is when Freyjadour Falenas had Oboro and his detective agency look into the mystery of the uprising of Lordlake. The clever little animal could track down a shady man threatening Norden for his silence, and lead the detectives to Salum Barows' Mansion, revealing who was really behind the whole plot.
Later on, Mr. Mouse helped Oboro with the capture of the thief Raven. The detective knew that Raven was interested in family trees and he set up a trap in Ceras Lake Castle's store room, with Egbert Aethelbald's precious family tree and grated cheese to make it easier for Mr. Mouse to bite the culprit red-handed.