The investigators notice the following ad in the morning paper:
"WANTED: Daring, experienced person or people to investigate difficult problem. May be dangerous. Call Hank at 420-4272 days or 421-1032 nights."
After responding to the ad, investigators meet with farmers Hank, Jake, Tony, Cynthia and Mary Jean regarding the death of their friend Johnny ODell. They suspect the involvement of someone called Dr. Menghin, who they claim is affiliated with some kind of cult. They say that Johnnys body was found next to a horrible jack-in-the-box toy, which they believe was meant as some kind of warning.
After an appointment with Menghin, the investigators search his office and discover incriminating evidence pointing to cult activity surrounding the Sumerian god Marduk, along with diagrams of a high-technology device created by Dr. Menghin for contacting the entity. The next day they learn that Dr. Menghin has been arrested for theft of plutonium.
In a final showdown in the basement of a Denver home, the investigators confront the farmers, and are themselves confronted by Monty Harbison, Menghins scientific assistant and leader of Menghins cult. It becomes clear that the farmers are in fact members of a cult which is opposed to Menghins, and that the death threats were coming from them all along. They were using the investigators in an attempt to infiltrate Menghins group and recover the Eye of Ras Al Ghethi, which had originally belonged to them. All of the farmers are killed by supernatural forces, and the investigators can see their bodies covering the floor of an adjacent room. Harbison demands the return of the Eye of Ras Al Ghethi, but the investigators pull a clever switcheroo using an object of identical size and shape, sealed in an envelope. Harbison discovers the trick, however, and kills all of the investigators.