Digital read-outs seem to be turning people's phobias into real-life nightmares, turning them into unstoppable killers. Mulder and Scully must find out what's happening and stop it before it's too late.

A 42-year old claustrophobic man steps into an elevator, sweating all over. Cramped up with other people he suddenly sees the words "Kill 'Em All" on the digital read-out of the elevator. This prompts him to perform a mass killing which brings agents Mulder and Scully in to investigate this bizarre case of a perfectly sane man.

Talking with the local sheriff, the agents discover that this is in fact the seventh similar killing which has caused 22 deaths in an area which is noted for being safe from drug dealers and masked murderers. Mulder cannot make any sense of what has gone on but does find that the digital display in the elevator has been smashed and he also finds a strange substance on the killer's fingers who was found dead outside the building.

Meanwhile, a woman named Mrs. McRoberts goes to have her car checked out in a garage late at night. Obviously scared of being raped she also suddenly sees a message on a computer screen telling her "He'll rape you, He'll kill you. Kill him first" which prompts her to kill the innocent repairman. Mulder turns up at the crime scene and also finds that the computer screen has been smashed.

Mulder and the sheriff go to talk to Mrs. McRoberts who also almost kills Mulder after seeing a message on her microwave. The sheriff, Spencer, kills her and when they analyse her body they discover that her adrenaline were 200 times more than usual and they also find an unknown compound on her adrenal glands. Scully concludes that these levels actually cause a substance which is similar to the drug, LSD.

Later while out jogging, Mulder spots a truck putting lots of flies into the gutter so he takes one of the flies to his paranoid friends, The Lone Gunmen. They tell him about LSDM which is an experimental insecticide that invokes a fear response among insects. While Mulder is out checking the fields, he is sprayed by a chemical from a helicopter. Mulder later concludes that something is sending subliminal messages to people which cause them to act bizarrely in response to their worst fears. He suggests that these people had been sprayed with the same chemical that Mulder was sprayed with which triggered off this response.

After investigating, the agents realize a postal worker named Ed Funsch who has been plagued with the messages all along and who is afraid of blood, is going to kill as a result of a worker who popped round to his house to take a voluntary blood sample.

They find that he has already climbed a tower at a nearby college and that he is firing at everyone with his rifle. Mulder goes up to the top of the tower where Funsch is. Ed stops shooting when he sees some blood on Mulder's wrist. Mulder takes him into custody.

Later, Mulder takes out his cellular phone and on the display it reads "All Done. Bye Bye.". The identity of the person who ran the experiment will now never be known....