The Warlock of Blackpool

From the introduction:

The Warlock of Blackpool is a one-shot adventure for D&D 5E targeted to characters levels 5-7. It is designed as a non-specific setting so that you can insert it as a brief detour into any approved campaign-in-progress where adventurers are traveling through mountains or forests. It also introduces the powerful NPC Dorian Cad'Fael, The Warlock of Blackpool, who will play a prominent role in future additional modules of a new overall campaign entitled The Legend of Blackpool.