Within London dwells humanoid monsters known as witches, which prey exclusively on men. To combat them, the British Secret Intelligence Service MI6 established a covert unit called RED, dedicated to witch extermination. Ruby Blood, a young genius witch hunter assigned to RED, is celebrated as the most talented operative the organization has ever produced. Off duty, she is a cheerful, food-loving girl who treasures time with her family and looks forward to her father’s home-cooked dinners every day. Her father, George Blood, was once a researcher at RED. Her younger sister, Amethyst, is an ordinary girl who adores their family. On Christmas night, Ruby’s life is shattered when Amethyst is transformed into a witch, forcing Ruby to confront the very monsters she hunts in a deeply personal struggle. Now she must fight to save her sister while navigating the dark underworld of witches, including the mysterious and powerful Victoria, known as the Cigar Witch, a legendary figure who disappeared a decade ago and who seems to have a hidden connection to Ruby’s past. As Ruby and her partner, fellow RED agent Rose, investigate, they uncover a web of secrets involving her father’s former work, the true nature of witches, and a looming threat that blurs the line between hunter and hunted. The story balances intense action and suspense with moments of warmth and humor, driven by Ruby’s dual life as a skilled fighter and a loving sister determined to reverse her family’s tragedy.