Warhammer Fantasy Roleplay: Enemy in Shadows Companion - Rules of Play says:

The Enemy in Shadows Companion is an indispensable guide to the first part of the epic Enemy Within campaign, the classic WFRP adventure that inspired a generation of gamers. Packed with additional rules, optional NPCs, tantalising adventure hooks, and wise words of advice for new and veteran GMs alike, it is the perfect addition to enhance your experience of the Enemy Within, or any other WFRP adventure.