Technically, Kate del Castillo has only signed on for the Halloween episode of Grimm. According to Hollywood Reporter, del Castillo will play Valentina Marquez, a "mysterious dectective from Albuquerque who comes to Portland to help Nick and Hank capture a serial child abductor. Valentina has spent the past five years tracking the perp and identifying patterns in related abductions."
Sound familiar? The episode is based on the legend of La Llorna, the tale of a mother who drowns her children so she can be with the man she loves. She is rjected by the man and kills herself in despair, but is cursed to wander the earth, forever searching for her children. FEARnet readers may recognize La Llorna as a popular attraction at Universal Studios's Halloween Horror Nights.
Del Castillo has an extensive list of credits from her home country of Mexico, and would be best known to American audiences for her role in Weeds.