The Claudandus Sect was a cult of stray cats who saw Claudandus as a holy figure. To honor him, they sacrificed themselves, committing suicide in his name.
A few days after moving into their new home and after finding the bodies of Sacha and Deep Purple, Francis hears a commotion in the upper levels of the house. He investigates and stumbles upon a cult of cats listening to their Cult Leader, sacrificing themselves to appease a holy cat called Claudandus. Hermann and Hermann, Kong, and Bluebeard were a part of this cult.
The cult was on the floor just below the attic and it's members were intolerant of outsiders. When Francis is discovered, they try and kill him.