In 1986 Phil Gallagher and Jim Bambra co-wrote the WFRP rulebook and The Enemy Within. However, earlier that year they also co-wrote Night’s Dark Terror for TSR. This was a D&D module designed to bridge the Basic and Expert sets. It is rightly regarded as a classic.
I have put together a comprehensive conversion of this for WFRP‘s first edition. It relocates the adventure to Kislev and makes a number of other changes, but is otherwise reasonably faithful. The document runs to nearly 50 pages and includes an appendix on spirits and animistic magic.
It can be freely downloaded from here in both PDF and editable Word formats.