A resurrected 18th-century witch named Serilda of Abaddon is confronted by Ichabod Crane and Detective Abby Mills. She seeks revenge by going after the descendants of those who condemned her. With the help of Ichabod's wife Katrina's vision, the two must act quickly to prevent Serilda from carrying out her lethal ritual. The unexplained resurrection of Officer Andy Brooks, in the meantime, raises the possibility of more sinister powers at work. The episode furthers the show's mythology by fusing historical intrigue with supernatural aspects as Ichabod and Abbie continue their efforts to avert the apocalypse.
In a terrifying vision, Ichabod Crane's wife Katrina alerts him to an approaching danger: Serilda of Abaddon, a vindictive witch. After being put to death during the Revolutionary War, Serilda has returned and is seeking retribution by going after the descendants of those who convicted her. Serilda wants to gather the ashes of her victims in order to regain her full strength as the Beaver Moon draws near.
Officer Andy Brooks, who was previously killed, is inexplicably brought back to life by a demonic entity. By presenting a magical medallion that aids in Serilda's resurrection, he helps to make her return possible.
By searching through Sheriff Corbin's classified documents, Ichabod and Lieutenant Abbie Mills learn more about Serilda's background and her role in the town's troubled past. The depth of Sleepy Hollow's supernatural foundations is shown by their inquiry, which takes them through secret passageways and historic archives. Ichabod and Abbie engage Serilda in a pivotal conflict as the Blood Moon rises, finally foiling her schemes and stopping additional carnage. By presenting fresh perils and emphasizing the heroes' developing cooperation in the face of supernatural threats, the episode expands the series' mythology.