Question: What is the use of exorcism in the Roman Catholic faith for those who are believed to be the victims of demonic possession, that has been depicted in a horror novel by Paul Tremblay?

Context articles: Irish Catholic Martyrs
Esmonde baronets
Anna Ecklund
Baptism of desire
A Head Full of Ghosts
Martha Broissier
Exorcism in the Catholic Church
The Exorcist (film)
Shrine (novel)
Legion (Blatty novel)

Irish Catholic Martyrs were dozens of people who have been sanctified in varying degrees for dying for their Roman Catholic faith between 1537 and 1714 in Ireland.
 The canonisation of Oliver Plunkett in 1975 brought an awareness of the other men and women who died for the Catholic faith in the 16th and 17th centuries.
 On 22 September 1992 Pope John Paul II proclaimed a representative group from Ireland as martyrs and beatified them.
 "Martyr" was originally a Greek word meaning “witness”.
 In the Acts of the Apostles, Peter, speaking to those in Jerusalem at Pentecost, claimed he and all the apostles were “martyrs”, that is, witnesses, in this case to Jesus's resurrection.
 Later the word came to mean a person who followed the example of Christ and gave up their lives rather than deny their faith.
The Esmonde Baronetcy, of Ballynastragh in the County of Wexford, is a title in the Baronetage of Ireland.
 It was created on 28 January 1629 for Thomas Esmonde.
 He raised a cavalry regiment for Charles I and commanded a regiment during the Siege of La Rochelle.
 Esmonde was the son of Sir Laurence Esmonde, who had abandoned the Roman Catholic faith during the reign of Queen Elizabeth and was raised to the Peerage of Ireland as Baron Esmonde in 1632.
 Lord Esmonde married firstly a Roman Catholic wife of the O'Flaherty family, and they had a son, Thomas, the first Baronet.
 She feared that the boy would be raised a Protestant and ran away with him, raising him as a strict Roman Catholic.
 As Thomas's father would not admit his legitimacy, (even though his father had no son by his second marriage) he was not allowed to succeed to the barony, which became extinct on his father's death in 1646.
 He did however gain possession of the family estates in County Wexford.
Anna Ecklund (sometimes documented as Emma Schmidt) was an American woman whose alleged demonic possession and exorcism occurred over several decades, culminating in an extensive exorcism that lasted from August 18 to December 23, 1928 in Earling, Iowa.
 Ecklund was said to have exhibited symptoms akin to possession beginning at age fourteen, and was forty six-years-old during her final exorcism by Father Theophilus Riesinger, a German Roman Catholic priest.
Baptism of desire (Latin: "Baptismus flaminis" ) is a teaching of the Anglican Communion, Lutheran Church and Roman Catholic Church explaining that those who desire baptism, but are not baptized with water through the Christian Sacrament because of death, nevertheless receive the fruits of Baptism at the moment of death if their grace of conversion included "divine and catholic faith", an internal act of perfect charity, and perfect contrition by which their soul was cleansed of all sin.
 Hence, the Catechism of the Catholic Church observes, "For catechumens [those instructed in the Catholic faith who are preparing to be baptized into the Catholic Church] who die before their Baptism, their explicit desire to receive it, together with repentance for their sins, and charity, assures them the salvation that they were not able to receive through the sacrament" (CCC 1259).
A Head Full of Ghosts is a horror novel by Paul Tremblay.
 The plot involves an American family under strain when their fourteen-year-old daughter, Marjorie Barrett, exhibits signs of mental illness.
 The story is told from the point of view of Marjorie's eight-year-old sister, Merry.
 Themes include elements of Catholic exorcism and reality television exploitation.
Martha Broissier (born 1556, died after 1578), was a French woman who was made famous around the year of 1578 for her feigned demonic possession at the age of 22.
 A fraud that was discovered by bishop Charles Miron, of which is either a Roman Catholic Diocese of Angers or a Roman Catholic Diocese of Orléans.
 According to Augustin Calmet, Martha was young woman and daughter of a weaver in Romorantin.
 She claimed to have been demonically possessed creating widespread circulation of the news in her time.
 Martha's case of demonic possession is often used by ancient theological historians in comparison with the Loudun possessions since both cases consist of convincing accounts of demonic possession yet are presumed to have been historically fraudulent affairs that reached the peak of fame.
Exorcism in the Catholic Church is the use of exorcism in the Roman Catholic faith for those who are believed to be the victims of demonic possession.
 In Roman Catholicism, exorcism is sacramental but not a sacrament, unlike baptism or confession.
 Unlike a sacrament, exorcism's "integrity and efficacy do not depend ... on the rigid use of an unchanging formula or on the ordered sequence of prescribed actions.
 Its efficacy depends on two elements: authorization from valid and licit Church authorities, and the faith of the exorcist."
 The Catechism of the Catholic Church states: "When the Church asks publicly and authoritatively in the name of Jesus Christ that a person or object be protected against the power of the Evil One and withdrawn from his dominion, it is called exorcism."
The Exorcist is a 1973 American supernatural horror film, adapted by William Peter Blatty from his 1971 novel of the same name, and starring Ellen Burstyn, Linda Blair, Max von Sydow, and Jason Miller.
 The film is part of "The Exorcist" franchise.
 The book, inspired by the 1949 exorcism of Roland Doe, deals with the demonic possession of a 12-year-old girl and her mother's attempts to win back her child through an exorcism conducted by two priests.
 The adaptation is relatively faithful to the book, which itself has been commercially successful (earning a place on "The New York Times" Best Seller list).
Shrine (1983) is a horror novel by English writer James Herbert, exploring themes of religious ecstasy, mass hysteria, demonic possession, faith healing and Catholicism.
 The story is about Alice Pagett, a deaf-mute child who's cured one night when she runs to an oak tree behind St. Joseph's, her local church.
 She's found by reporter Gerry Fenn and, when news of her cure spreads, their village becomes ablaze with publicity.
 After Alice performs several "miracle" cures in front of the tree, and claims to have seen the Virgin Mary there, it starts to be treated as a Lourdes-like shrine by Catholic pilgrims. St. Joseph's priest, Father Hagan, however, senses spiritual danger.
Legion is a 1983 horror novel by William Peter Blatty, a sequel to "The Exorcist".
 It was adapted into the movie "The Exorcist III" in 1990, and is part of The Exorcist franchise.
 Like "The Exorcist", it involves demonic possession.
 The book was the focus of a court case over its exclusion from "The New York Times" Best Seller list.