"A Reaper at the Gates" is the third book in the "An Ember in the Ashes" series written by Sabaa Tahir. The series is a popular young adult fantasy series that blends elements of dystopia, magic, and adventure. The first book in the series, "An Ember in the Ashes," was published in 2015 and gained significant attention and praise for its compelling characters and intricate world-building.

Here's a brief overview of the series and the third book:

1. "An Ember in the Ashes" (2015): The story is set in a brutal, militarized empire inspired by ancient Rome. It follows the lives of two main characters, Laia, a young scholar who becomes a spy, and Elias, a highly skilled soldier with a conscience. They are both caught up in a world of violence, oppression, and political intrigue. The book explores themes of power, freedom, and resistance.

2. "A Torch Against the Night" (2016): The second installment continues the journey of Laia and Elias as they navigate a treacherous world filled with danger and betrayal. They are pursued by a ruthless and enigmatic commandant as they seek to rescue Laia's brother from a notorious prison.

3. "A Reaper at the Gates" (2018): In the third book, the characters' destinies become even more intertwined as they face new challenges and adversaries. The story delves deeper into the conflict between the ruling Martials and the oppressed Scholars, and the supernatural elements of the world come into play. The characters must make difficult choices that will shape the fate of their world.