Leland is a nice old man some think. He lets a boy get a Mickey Mantle baseball card for next to nothing providing the boy performs mischief at another person's house. Leland sets people against each other. He finds their weakness and then uses someone else to set up situations that people's enemies will be blamed for. The result is death and mayhem. Leland is the devil of course and Castlerock is his home for a bit.

Leland finds one true adversary in the towns Sheriff. The Sheriff investigates Leland's store and finds newspaper clippings of major disasters throughout the world with Leland in pictures of many of those articles. Leland has his fun with the town's hero by framing him for crimes and seducing his wife.

In a final showcase of Leland's master plans of manipulation, the town runs amuck with death everywhere. Rival preachers tell each other to go to hell and prepare to kill each other to symbolize just how far down the path to madness the town has gone. Amidst the madness the Sheriff shoots in the air to calm the crowd. He points at Leland and shows the town how they have been manipulated into hating and fearing one another.

Leland does have a true disciple whom he hopes will rescue his plans and wreck true havock. His name is Buddy, a man who likes to gamble and feels guilt after killing his own wife. Leland has equipped him with explosives and instructed him to destroy the town. The Sheriff tells Buddy he doesen't have to do it, but Leland responds "Yes you do, yes you do." After some thinking Buddy comes charging at Leland and detonates himself in the hopes of killing Leland. The devil emerges without a scratch and congratualtes his antagonist the sherrif on his success. The devil states he will visit the sheriff's yet to be born son in the future and even gives a date.

The movie was one of great oneliners by the devil. The master manipulations of townsfolk via small deeds for treasures was truly clever. Often just one little act could turn people to finally killing their enemies even if their enemies were not actually responsible. Needful things is a horror film based on a Stephen King novel with a sense of humor to say the least.