Children of the Corn

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In September 1963, the town of Gatlin, Nebraska, is suffering a severe drought. In a tent out in the vast cornfields, a boy preacher (Robert Gerdisch), claims that an Old Testament-era Canaanite God whom he calls "He Who Walks Behind the Rows" has spoken to him in his dreams. He tells the other children that the sinful adults are the reason for the drought, prompting them to kill everybody over the age of nineteen in town. They then establish a death cult with the prime rule that, upon reaching the age of nineteen, one must be sacrificed to the cult's God.
In April 1975, twelve years later, a bickering couple, Vietnam veteran Burt (David Anders) and his wife Vicky (Kandyse McClure), are driving along a back road near Gatlin, planning on celebrating their second honeymoon in California, when a boy named Joseph (Remington Jennings) stumbles out of the roadside corn and in front of their car. After accidentally running Joseph over, Burt assesses the body and realizes the boy's throat was slashed. After wrapping and placing the body in the trunk, Burt tells Vicky to wait for him while he looks around with shotgun in hand. Among the corn, Burt finds Joseph's bloodied suitcase and takes it with him back to the car. He and Vicky drive off in search of aid, not realizing they are being watched by Isaac (Preston Bailey), the 9-year old current cult leader, and his most loyal follower, 18-year-old warrior Malachai (Daniel Newman).
After hearing a group of children giving an evangelical sermon over the radio, Burt and Vicky reach an abandoned gas station. After finding the phones non-functional Burt decides to go to Gatlin. While Burt drives, Vicky manages to open Joseph's suitcase and finds an amulet inside which she recognizes as a pagan creation. Meanwhile, in the cornfields, Isaac tells the others about Burt and Vicky and that they, like the "blue man" (a police officer who was crucified for trying to stop them) must be killed to appease "He Who Walks Behind the Rows", who demanded Joseph be killed for trying to escape.
Reaching the town, Burt and Vicky find it seemingly abandoned, the stoplight dead, with a calendar in a bar still reading 1963. Eventually coming across a church with a sermon board dated last week, Burt goes in to investigate, ignoring Vicky's pleas that they should just leave (and taking her keys after she threatens to abandon him). Inside the church, Burt finds various occult drawings, a larger version of the trinket in Joseph's suitcase and a book listing the birthdays of the town's inhabitants.
As Burt skims through the book, Vicky is surrounded and attacked by Malachai and several other boys (directed from a rooftop by Isaac). She manages to kill one of them with Burt's shotgun before Malachai stabs her. Hearing the shotgun blast, Burt rushes outside just as Malachai blows the car up. Chased by the children into an alleyway Burt is taunted by Isaac who throws a knife at him which hits him in the arm. Killing two of the older boys, Burt runs off into the cornfields, where the children refrain from going without either Isaac or Malachai.
In the alleyway, Isaac confronts Malachai, telling him that by spilling Joseph's blood in the corn he angered He Who Walks Behind The Rows. After questioning Malachai's faith, Isaac has him pray before they regroup with their followers, who they tell must sacrifice Burt in the clearing where the blue man's corpse is held. After leading a song, Malachai and the children begin hunting Burt through the corn.
While searching, Malachai is told by Nahum (Paul Butler, Jr.), one of the younger boys, that he had a vision of He Who Walks Behind the Rows, leading Malachai to believe Nahum will be the new prophet when Isaac's time comes to an end. Before leaving to continue the search for Burt (who had overheard the entire conversation), Malachai mentions that they must finish the search before dark, as that is He Who Walks Behind the Row's time.
Having lost a large amount of blood due to his arm injury, Burt begins having flashbacks to Vietnam and kills several of the children, including Nahum. At nightfall the worshipers abandon the search and return to the town. They have a feast prepared by the females, who seem concerned that Burt was not apprehended. Later that night, Isaac holds a sermon in the church based on the tenet of "be fruitful and multiply" and proclaims that the time of fertilization has come. He beckons a teenage girl (Zita Vass) and boy (Jake White) up to the front of the church and they immediately disrobe and have sex in front of the entire congregation, much to their excitement.
In the fields, Burt, lost and delusional, has visions of all those he has killed, and begins wandering around aimlessly, searching for the road as the plant life begins attacking him. Soon, Burt finds the clearing and discovers Vicky who, like the blue man, has been made into a scarecrow. Hallucinating that Vicky's body is talking to him, Burt is faced by He Who Walks Behind The Rows, who proceeds to disembowel him and rip his eyes out in a form of ritual sacrifice.
The next day, Isaac tells the children that He Who Walks Behind The Rows is displeased with their inability to kill Burt, who He had to dispose of Himselfâlike the blue man (who, when killed, reduced the 'age of favor' from twenty to nineteen). Isaac informs everyone that the age of sacrifice has been lowered from nineteen to eighteen as punishment for their failure. After the children leave Isaac stands in front of the a pile of the children's bodies and as he sets them on fire he looks at something and shouts "Scarecrow!". The scarecrow is revealed to be Burt.
Later, Malachai and the other eighteen-year-olds enter the cornfields at dusk, offering themselves to He Who Walks Behind the Rows. While saying goodbye, Malachai's pregnant lover Ruth (Alexa Nikolas), whose faith had earlier been shaken, has a vision of herself setting fire to the corn.

Question: Who was giving an evangelical sermon?
Answer: Children.