Justus Frankce is the Baron of Ussingen and is allied with a unnamed Nurgle cult. He fled Ussingen before it was attacked by the Rotblood Tribe. His manor, which was used by the Rotbloods to store supplies, is destroyed in Empire in Flames.
According to dialogue between Markus Kruber and Victor Saltzpyre at the start of Empire in Flames, Victor previously had an encounter with the Baron. The Baron was accused of blasphemy in an incident with his mistress and was offered a choice by the Witch Hunter: either give half his wealth to the Church of Sigmar, or burn on a witch pyre instead of the mistress. The Baron chose the former.