Cloistered Beast

From publisher blurb:

A humble merchant of the city was poisoned by a terrible beast. During a return from a business trip, he was surprised by a storm and took shelter under the trees where he found the beast that attacked and poisoned him. Despite the non-human looking, the beast told the merchant that it could cure him if he offers it someone with whom he had close bond of blood. Upon returning to the city, sick by the creature's venom, the merchant started to recruit hirelings to fight the monster and bring the antidote as soon as possible.