Plot summary
Nine months have passed since Katrina's death. A woman named Pandora encounters the Headless Horseman, seals him within a mysterious box, and summons a yaoguai, a demon that feeds on the fear of its victims. Ichabod reaches out to Abbie (who is now an FBI agent) after he is arrested and detained for smuggling an artifact into the United States. When Abbie arrives to collect him, he reveals Katrina's pendant, which is linked to the Horseman's power, has warned him of the latter's disappearance, meaning a new threat has emerged. The two are subsequently drawn into an investigation of a double homicide with both victims having shown great fear before they were killed. Ichabod leads Abbie and Jenny to a message left by his fellow agent Betsy Ross, which reveals the demon is drawn to the smell of gunpowder.
Credits
Adapted from Wikipedia contributors, Sleepy Hollow season 3. HTML formatting and reference markers removed.