Where a person files a cross-complaint as authorized by Section 428.10, he may unite with the cause of action asserted in the cross-complaint any other causes of action he has against any of the cross-defendants, other than the plaintiff in an eminent domain proceeding, whether or not such cross-defendant is already a party to the action.
Source:
Section 428.30, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=428.30..