[plot description by original author]
The Hook, Line and Sinker format appeared in SHADIS magazine:Hook: The current location or situation of the party.
Line: The situation which introduces the side-adventure.
Sinker: The twist, or what is unknown to the party, and the result.
HOOK: The party has learned about a small dungeon made of natural rock caverns and has decided to explore it.
LINE: Upon reaching this wilderness location, they discover a homestead isolated from the rest of civilization (possibly subject to frequent monster raids). The peasant family is pleasant enough but appears to be hiding something. . .
After the party begins exploring the actual dungeon and has repelled gruesome animal beasts they find a room that holds a little girl. She cannot be more than 6 years old, has matted and grimy hair, and is wearing furs. She obviously has made her home in this part of the dungeon, but how, with all those monsters running around?
SINKER: If the party tries to coax the girl back to the outside world, she will resist. If they drag her to the surface, and a moon is near a full or half phase, the little girl turns into a werewolf! This explains why the dungeon beasts would avoid her; she "smells" dangerous.
The peasant family will confess that their 25-year-old daughter had a liaison with a visiting hunter several years ago--and he happened to be were! (A half-breed child born lycanthropic may differ in some ways from your game's monster listings.) If the party kills or seriously injures the little girl, they will later encounter a vengeful werewolf, who still takes an interest in his bastard daughter's health and safety. The family may not realize that some spells cure lycanthropy, and would be grateful if the party arranged for such a spell to be cast on their daughter.