"Needful Things" opens in the town of Castle Rock, Maine, sparking the curiosity of its citizens. The proprietor, Leland Gaunt, is a charming elderly gentleman who always seems to have an item in stock that is perfectly suited to any customer who comes through his door. The prices are surprisingly low, considering the merchandise - such as a rare Sandy Koufax baseball card, a carnival glass lampshade, and a fragment of wood believed to be from Noah's Ark - but he expects each customer to also play a little prank on someone else in Castle Rock. Gaunt knows about the long-standing private grudges, arguments, and feuds between the various townspeople, and the pranks are his means of forcing them to escalate until the whole town is eventually caught up in madness and violence.