Question: Who wrote the 1986 novel that the 2017 horror movie is based on that features the actor from Hemlock Grove? 

Context articles: Emilia McCarthy
List of Hemlock Grove episodes
Bill Skarsgård
Nathan Barr
Coney Rock
Hemlock Grove
Pennsylvania Route 790
Penelope Mitchell
It (2017 film)
Hemlock Grove (TV series)

Emilia McCarthy (born August 28, 1997) is a Canadian actress, dancer and writer.
 She played the daughter of the sheriff in the television series Netflix called "Hemlock Grove".
 McCarthy also played Taylor Dean in the movie "Zapped" of Disney Channel Original Movie.
"Hemlock Grove" is an American supernatural drama series developed by Brian McGreevy and Lee Shipman, based on McGreevy's novel of the same name.
 The first season premiered exclusively via Netflix's web streaming service on April 19, 2013.
 The second season premiered on July 11, 2014.
 The third and final 10-episode season premiered on October 23, 2015.
Bill Istvan Günther Skarsgård (born 9 August 1990) is a Swedish actor and model, known for his roles in "Simple Simon", "Hemlock Grove", "Atomic Blonde" and Pennywise the Dancing Clown in the 2017 film "It".
Nathan Barr (born February 9, 1973; also known as Nate Barr) is an American film and television composer known for playing the majority of the instruments heard in his compositions.
 While he is best known for scoring all seven seasons of HBO's Emmy Award-winning series, "True Blood", Barr has recently composed music for FX's "The Americans" and Netflix's "Hemlock Grove".
 On July 18, 2013, Barr garnered a double Emmy nomination for "Outstanding Original Main Title Theme Music" based on his work on "The Americans" and "Hemlock Grove".
Coney Rock is a 600 foot tall, 1,000 foot long, glacially formed granite and gneiss ridge in Storrs, Connecticut, part of the town of Mansfield.
 It is part of the 200-acre Coney Rock Preserve owned partly by the Town and partly by Joshua's Trust that includes the remains of an old farm, a marsh, a hemlock grove, a hornbeam stand, a birch grove, and glacial erratics, as well as five miles of white and yellow blazed trails.
 There is a memorial bench at the peak.
 According to local legend, one can see Rhode Island from the ridge.
 The cliff is stepped.
Hemlock Grove is a 2012 Horror-thriller debut novel by American author Brian McGreevy.
 The book was released on March 27, 2012 through Farrar, Straus and Giroux and is set in the fictional town of Hemlock Grove, Pennsylvania.
 A graphic novel tie-in and a television series based on the events in the book have been produced.
Pennsylvania Route 790 was a state highway in the county of Pike in Pennsylvania, USA.
 The highway's southern terminus was at State Route 290 south of Hemlock Grove.
 The highway progressed northward along Hemlock Grove Road, passing through Hemlock Grove and into Greentown, where it terminated at an intersection with State Route 507.
 The highway was assigned in 1930 and decommissioned in the 1946 removal of state highways.
Penelope Mitchell (born 24 July 1991) is an Australian actress best known for playing the role of Letha Godfrey on the American horror television series "Hemlock Grove" and Liv Parker on "The Vampire Diaries".
It: Chapter One, or simply It, is a 2017 American supernatural horror film directed by Andy Muschietti, based on the 1986 novel of the same name by Stephen King.
 The screenplay is by Chase Palmer, Cary Fukunaga and Gary Dauberman.
 The first of a planned duology, the film tells the story of seven children in Derry, Maine, who are terrorized by the eponymous being, only to face their own personal demons in the process.
 The novel was previously adapted into a 1990 miniseries.
Hemlock Grove is an American Netflix original horror web television series.
 Executive produced by Eli Roth, developed by Brian McGreevy and Lee Shipman, and a production of Gaumont International Television, the series is based on McGreevy's novel of the same name.
 The show premiered April 19, 2013, with all 13 episodes made immediately available for online viewing.