Harper Lee, whose single work of fiction, To Kill a Mockingbird, earned her the National Medal of Freedom and the distinction of having written one of the bestselling novels ever published, is going to be releasing a second book. According to the Associated Press, Go Set a Watchman, which Lee completed in the 1950s, will be published by HarperCollins in July.

The manuscript, the AP said, was found recently and is "essentially" a sequel to To Kill a Mockingbird. The 304-page work will mark Lee's first release in over 50 years.

According to Harper, Go Set a Watchman is set roughly 20 years after To Kill a Mockingbird and follows the young heroine from that novel, Scout, as an adult.

When Scout travels to her small Southern town of Maycomb, from New York City, to visit her father, Atticus, she is, Harper explained, "forced to grapple with issues both personal and political as she tries to understand both her father’s attitude toward society, and her own feelings about the place where she was born and spent her childhood."

Lee said, in Harper's release, that she felt the novel is "a pretty decent effort." Speaking to the manuscript's abrupt appearance, Harper said the work was set aside by Lee after To Kill a Mockingbird was published and "never returned to" by the author.

Considered lost, the manuscript was discovered in 2014 by Lee's lawyer and friend, Tonja Carter, who, Harper noted, stumbled upon it in "a secure location" where it had "been affixed to an original typescript of To Kill a Mockingbird." Lee said of Go Set a Watchman: "After much thought and hesitation I shared it with a handful of people I trust and was pleased to hear that they considered it worthy of publication. I am humbled and amazed that this will now be published after all these years."

To Kill a Mockingbird, originally published in 1960, continues to be remarkably popular; in 2014 it sold over 382,000 copies in mass market paperback, and about 65,000 in trade paperback, according to Nielsen BookScan, which tracks approximately 80% of print sales.

Go Set a Watchman has also been acquired in the U.K., by CEO of Penguin Random House there, Tom Weldon, and PRH UK plans to publish Go Set a Watchman on the same day as Harper: July 14, 2015.

Note: This story has been updated from its original vesion to reflect the release of additional information.