This is Robert Louis Stevenson's historical romance set during the War of the Roses.

Set in England during the fifteenth-century Wars of the Roses, this swashbuckling historical novel by the author of Treasure Island and Kidnapped tells the story of young Dick Shelton. Betrayed by his treacherous and brutal guardian, Sir Daniel Brackley, Dick seeks the help of John Amend-All, leader of the mysterious fellowship of the Black Arrow―and Brackley's sworn enemy. Pitted against fierce fighters, a treacherous priest, and Sir Daniel, Dick seeks to become a knight and rescue his true love.
Brimming with adventure, suspense, and romance, this thrilling tale presents a classic portrait of England during one of its most tumultuous eras, as Dick is pulled by his loyalties to the houses of both York and Lancaster. He must make a crucial choice, for his fate and the fate of England hang in the balance.