Short answer
Good Fellow names two different things: a Book writing perk that increases the zombie limit before a PR penalty, and a side quest involving the Head of the Village. Match the name to the talent tree or quest journal before following an unlock route.

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The zombie-limit perk
Good fellow is in the Book writing talent tree. It costs 1 Book writing inspiration point and follows a Book writing mastery +1 node. Happy supplier follows this perk.
Its described effect raises the number of zombies you can keep before receiving a PR penalty. The talent-tree source does not give a numeric cap, so check your current game tooltip before planning a larger workforce.
The Village side quest
The Good Fellow side quest needs at least 10 Village reputation. What the Fairy? unlocks it; Dust in the Kitchen precedes it in the journal.
Ask Januarius at the Village Tavern to call the Head of the Village. The next quest is Dungeons and... that's it, probably.; this route leads toward finding the Plague Doctor and obtaining Dream Dust.
Choose your next guide
For an excessive-zombies penalty, follow the zombie-limit and inspiration guides. For the fairy storyline, follow Dream Dust. Completing the side quest and buying the talent are separate objectives.
Sources
- communityWikily: Book writing talent tree
- communityWikily: Good Fellow side quest

