On a quiet, uneventful day, Summer applies for a part-time job for a dapper man named Mr. Lucius Needful. His little store, Needful Things, deals with exotic items for your everyday desires. Mr. Needful helps any wayward customers who wanders into his shop. Trying to get over your messy divorce? He's got a cologne that will instantly attract any woman within range. Want to improve your sports skill? His basketball might be the ticket. Miracles upon miracles, the objects grant the user anything they could ever hope, free of charge. It's as if a guardian angel has descended upon their sleepy town to lift the weight off their shoulders.
But when an itch needs to be scratched, there's only one kind: a Mr. Scratch. People soon return to Needful Things to complain. That cologne indeed attracted a lot of women, but the customer is now impotent. That microscope may have satisfied a starving scientist, but he would have been mentally impaired after using it. Lucius' items come at a price, for anyone who makes a deal with the Devil pays it.
The only person who sees through his ruse is Rick. Taking the microscope that would have ripped him of his genius, Rick uses it to create a panacea to Lucius' cursed objects. This cures the people of their ailment through science while keeping the awesome abilities the objects granted. It's so successful that it puts Needful Things out of business. Saddened that a mortal beat him at his own game, Lucius tries to kill himself. His only support comes from Summer who saves him in time. Resentful that her grandfather does not respect her, Summer vows to help Lucius retool his shop as a gesture of kindness for all the times he's been nice to her.
Lucius and Summer successfully turn their shop into N33dful.com, an online goods store. Google instantly buys their company, making the two very rich. Lucius quickly betrays Summer by cutting her off, citing no matter how many good deeds one does, he is still the devil.
In an effort to make up for his behavior, Rick takes Summer out to train. The two bulk up, then proceed to beat up Lucius as revenge. Bet the Devil didn't see that coming.