What is the fourth novel in the cycle of books focused  on the adventures of a teenage boy named Eragon?
Inheritance
Inheritance Cycle
The Inheritance Cycle is a young adult tetralogy of high fantasy novels written by American author Christopher Paolini.
 Set in the fictional world of Alagaësia ( ), the novels focus on the adventures of a teenage boy named Eragon and his dragon, Saphira, as they struggle to overthrow the evil king Galbatorix.
 The series was originally intended to be a trilogy (named the "Inheritance Trilogy") until Paolini announced on October 30, 2007, while working on the third novel, that he believed the story was too complex to conclude in just three books.
Inheritance (Paolini novel)
Inheritance is a 2011 novel written by American author Christopher Paolini.
 It is the fourth novel in the Inheritance Cycle.
The Diamond Brothers
The Diamond Brothers is a series of humorous children's detective books by Anthony Horowitz, the first of which was published in 1986.
 The books tell the adventures of the world's worst private detective, Tim Diamond, and his younger brother, Nick Diamond, who is considerably more intelligent.
 These books are aimed at young teenagers, slightly younger than those aimed at with the more recent "Alex Rider" series.
 However, both series star a teenage boy and include guns, fights and worldwide criminals.
 The most notable difference is that "The Diamond Brothers" series contains much more humour, with many puns, pop culture references and absurd situations.
 Although the books started in the late 1980s and have continued into the millennium, Nick and Tim remain roughly the same age (14 and 28 respectively), while London changes with the times (the newer books feature Oyster Cards and computers for example, whereas the older books feature parts of London that have long since changed, such as smoking in offices). List of Rainbow Magic books
Over 200 Rainbow Magic books have been published since 2003.
 Each series includes 4 or 7 books focused on a central theme.
 Daisy Meadows has also started a book series "Magic Animal Friends" that was released on 3 July 2014 with four books: "Lucy Longwhiskers Gets Lost", "Molly Twinkletail Runs Away", "Ellie Featherbill All Alone" and "Bella Tabbypaw in Trouble" and also a special named "Poppy Muddlepup's Daring Rescue".
 Many more books of Magic Animal Friends such as Sophie Flufftail, Emily Prickleback, Ruby Fuzzybrush and Rosie Gigglepip were released on 5 April 2015. Big Wolf on Campus
Big Wolf on Campus was a Canadian television series created by Peter A. Knight and Christopher Briggs that ran from 1999 to 2002.
 The central plot revolves around a teenage boy named Thomas "Tommy" P. Dawkins, who was bitten by a werewolf during a camping trip in the woods a week before his senior year of high school.
 After the bite transforms him into a werewolf, he fights against vampires, cat women, ghosts, zombies, and other supernatural entities to keep his hometown of Pleasantville safe - even though almost everyone in Pleasantville believes that their protector, dubbed ""The Pleasantville Werewolf"", is dangerous. Jing: King of Bandits
Jing: King of Bandits (Japanese: 王ドロボウJING , Hepburn: Ō Dorobō Jing , lit.
 "King of Bandit Jing") , is a Japanese manga series written and illustrated by Yuichi Kumakura.
 The series was originally serialized in Kodansha's "Comic Bom Bom" magazine from 1995 to 1998; the publisher later collected the individual chapters into seven tankōbon volumes.
 The series continued in Kodansha's "Magazine Z" in 1999, under the title KING OF BANDIT JING, known as Jing: King of Bandits: Twilight Tales outside of Japan and ran until finishing in 2005.
 The story revolves around a teenage boy named Jing who despite his young age is known as the "King of Bandits".
 Along with his partner Kir, a talking albatross, he travels the world in search of new adventures and legendary treasure.
 Throughout the series the duo manage to pull off impossible heists and outwit countless enemies that stand in their way. More Than This (novel)
More Than This is a young adult novel by Patrick Ness, published by Candlewick Press in 2013.
 It follows a teenage boy named Seth who, after drowning in the ocean, wakes up alone on a desolate suburban English street in what he believes to be hell. Willy/Milly
Something Special (also known as "Willy/Milly" and "I Was a Teenage Boy") is a 1986 comedic fantasy film directed by Paul Schneider, based upon a story by the same name by Alan H. Friedman.
 The film follows the title character of Milly Niceman, a young tomboy who is unhappy with the traditional expectations for her gender and longs to become a boy so she can act however she wants.
 Initially released as "I Was a Teenage Boy" in 1986, the film was later re-titled to "Something Special" for a 1987 limited theatrical release and for a VHS release. The Last Book in the Universe
The Last Book in the Universe (2000) is a post-apocalyptic science fiction novel by Rodman Philbrick.
 Set in a cyberpunk dystopia, its protagonist and narrator is a teenage boy named Spaz who suffers from epilepsy. Ranma ½
Ranma ½ (Japanese: らんま 1/2 , Hepburn: Ranma Nibun-no-Ichi , pronounced "Ranma One-Half") is a Japanese manga series written and illustrated by Rumiko Takahashi.
 It was serialized in "Weekly Shōnen Sunday" from September 1987 to March 1996, with the chapters collected into 38 "tankōbon" volumes by Shogakukan.
 The story revolves around a teenage boy named Ranma Saotome who has trained in martial arts since early childhood.
 As a result of an accident during a training journey, he is cursed to become a girl when splashed with cold water, while hot water changes him back into a boy.
 Throughout the series Ranma seeks out a way to rid himself of his curse, while his friends, enemies and many fiancées constantly hinder and interfere.