Question: Who developed the plot for the series of children's fantasy novels about Fireheart and Graystripe of the Thunderclan?

Context paragraphs:
Forest of Secrets: Forest of Secrets is a children's fantasy novel, the third book in the original "Warriors" series, written by Cherith Baldry under the pen name of Erin Hunter.  The plot is about Fireheart, a ThunderClan warrior, attempting to prevent his best friend Graystripe from falling in love with Silverstream, whom Graystripe is not allowed to fall in love with.  Silverstream later dies giving birth to Graystripe's kits.  When RiverClan claims the kits, Graystripe makes the difficult decision to join RiverClan.  Fireheart also becomes deputy after Tigerclaw, the deputy, attempts to kill the leader, Bluestar.  The main theme of the book is forbidden love.  "Forest of Secrets" takes place in a fictional forest based on many natural locations.

A Dangerous Path: A Dangerous Path is a children's fantasy novel, the fifth book in the "Warriors" series, written by Cherith Baldry and Kate Cary under the pseudonym of Erin Hunter.  This individual book was written by Cherith Baldry.  The series is about four Clans of wild cats, and their adventures in the forest in which they reside.  The story follows a plan set up by Tigerstar, leader of ShadowClan, who wishes to destroy ThunderClan by using dogs to hunt them down.  At the end of the book, Bluestar, leader of ThunderClan, dies after risking her life to kill the dogs, making Fireheart, now Firestar, the new leader of ThunderClan.  Near the end of the book, Fireheart's friend Graystripe also returns to ThunderClan from RiverClan, knowing that no one will respect him in RiverClan.

Lloyd Alexander: Lloyd Chudley Alexander (January 30, 1924 – May 17, 2007) was an American author of more than forty books, primarily fantasy novels for children and young adults.  His most famous work is "The Chronicles of Prydain", a series of five high fantasy novels whose conclusion, "The High King", was awarded the 1969 Newbery Medal for excellence in American children's literature.  He won U.S. National Book Awards in 1971 and 1982.

Fire and Ice (Hunter novel): Fire and Ice is a children's fantasy novel, the second book in the "Warriors" series, written by Kate Cary under the pen name of Erin Hunter.  The plot centers around Fireheart and Graystripe, newly promoted warriors of ThunderClan, which is one of the four groups of feral cats living in the wilderness.  Fireheart learns that his best friend Graystripe has fallen in love with Silverstream, a warrior from RiverClan, even though it is against the cats' "warrior code".

Into the Wild (novel): Into the Wild is a children's fantasy novel written by Erin Hunter after concepts and outlines created and developed by Victoria Holmes.  The novel was published by HarperCollins in Canada and the United States in January 2003, and in the United Kingdom in February 2003.  It is the first novel in the "Warriors" series.  The book has been published in paperback, and e-book formats in twenty different languages.  The story is about a young domestic cat named Rusty who leaves his human owners to join a group of forest-dwelling feral cats called ThunderClan, adopting a new name: Firepaw.  He is trained to defend and hunt for the Clan, becomes embroiled in a murder and betrayal within the Clan, and, at the end of the book, receives his warrior name, Fireheart, after a battle with another Clan.  The novel is written from the perspective of Fireheart (previously known as Rusty for a short time, then, for most of the book, Firepaw).

Rising Storm (novel): Rising Storm is a children's fantasy novel, the fourth book in the "Warriors" series, written by Cherith Baldry and Kate Cary (Plus two others) under the pen name of Erin Hunter.  "Rising Storm" was written by Kate Cary.  The series follows the adventures of four Clans of wild, anthropomorphic cats.  In the previous book, "Forest of Secrets", Graystripe's mate, Silverstream, died while giving birth.  ThunderClan and RiverClan fought over the two kits, seeing as the mother of the kits, Silverstream, was the daughter of the RiverClan leader, Crookedstar, and the father was Graystripe, a ThunderClan warrior.  Graystripe decided to join RiverClan, despite knowing he will be shunned there.  In "Rising Storm", Fireheart has to tackle his new duties as deputy, knowing that the old one, Tigerclaw, who had been exiled, is in the forest somewhere, seeking revenge against Fireheart, Bluestar, and ThunderClan.  At the end of the book, Tigerclaw becomes leader of ShadowClan and receives the name Tigerstar, finally achieving the position he killed for.  The main theme in the book is power.  The forest in the book is inspired by multiple natural locations, such as the New Forest, in southern England.

Sunset (novel): Sunset is a children's fantasy novel, the sixth and final book in Erin Hunter's "Warriors: The New Prophecy" series.  The book begins with the group of cats known as ThunderClan rebuilding its camp with the help of its old friends Stormfur and Brook following a badger attack in "Twilight".  As the book progresses, BrambleClaw and Squirrelflight overcome a previous conflict and fall in love again, but Brambleclaw continues to visit the spirit of his evil father Tigerstar in his dreams.  Brambleclaw manages to convince ThunderClan leader Firestar to choose a new deputy to replace the long missing Graystripe and is surprised when he is chosen.  Brambleclaw's half-brother Hawkfrost attempts to kill Firestar in order that Brambleclaw might become leader of ThunderClan, but Brambleclaw saves Firestar and kills Hawkfrost, fulfilling the prophecy "Before there is peace, blood will spill blood and the lake will run red".

Warriors (novel series): Warriors is a series of novels published by HarperCollins; it is written by authors Kate Cary, Cherith Baldry, Tui Sutherland, with the plot developed by editor Victoria Holmes, who collectively use the pseudonym Erin Hunter.  The series follows the adventures of four Clans of wild cats—ThunderClan, ShadowClan, WindClan, and RiverClan —in their forest and lake homes, who look up to StarClan, their warriors ancestors, and spirits in the stars, who guide the four clans.  SkyClan, the long-forgotten fifth Clan of the forest, is later introduced in the stand-alone novel "Firestar's Quest".  It receives additional focus in the novel "SkyClan's Destiny", the manga trilogy "SkyClan and the Stranger", and the 2013 novella "Cloudstar's Journey".

Warriors (arc): Warriors: The Prophecies Begin is the first story arc in the "Warriors" juvenile fantasy novel series about anthropomorphic feral cats.  The arc comprises six novels which were published from 2003 to 2004: "Into the Wild", "Fire and Ice", "Forest of Secrets", "Rising Storm", "A Dangerous Path", and "The Darkest Hour".  The novels are published by HarperCollins under the pseudonym Erin Hunter, which refers to authors Kate Cary and Cherith Baldry and plot developer/editor Victoria Holmes.  The sub-series details the adventures of the housecat Rusty, who joins ThunderClan, one of four Clans of feral cats living in a forest which adjoins the human town in which he originally lives.  The arc's major themes deal with forbidden love, the concept of nature versus nurture, and characters being a mix of good and bad.  Though the novels have appeared on the "New York Times" Bestseller List and have been nominated for several awards, none of the novels in the "Warriors" sub-series have won a significant literary award.

Warrior's Refuge: Warrior’s Refuge is the second in an original English-language manga trilogy based on the best-selling book series "Warriors" by Erin Hunter.  The manga was published by the distributor Tokyopop, and was released on December 26, 2007 along with Dark River, the second book in "Warriors: Power of Three".  It follows Graystripe and Millie as they journey to find ThunderClan.  It is drawn by James Barry.

Supporting paragraphs: Fire and Ice (Hunter novel) Warriors (novel series)
Answer: Victoria Holmes