A team of surveyors hired to map the tunnels beneath SleepyHollow discover a long abandoned trapdoor which has beenhiding... something... that quickly overpowers them. Followingthe men's disappearance, Crane and Mills are called in toinvestigate. Ichabod and Abbie follow the men's trail to therune-marked trapdoor, and discover a huge underground vault -the "Fenestella" - which appears to have beendesigned by Founding Father and Masonic architect ThomasJefferson. After consulting Grace Dixon's journal, the TwoWitnesses learn that the vault - which was clearly designed toconceal something of high value to the revolutionary cause - isnow also occupied by something (or things) originally meant toprotect the unknown treasure kept inside, but on whom thecenturies of mystical concealment has taken a decidedly eviltoll. As Crane and Mills descend deeper below ground to try andrescue the missing men before it's too late, they make anotherstartling discovery as they come face-to-face with an ally theycould never have anticipated, who has information vital to theTwo Witnesses' overarching mission. But securing thatinformation, rescuing their quarry and destroying their foesmay prove to be an impossible task. Meanwhile, Frank Irvingapproaches Jenny with a seemingly innocent favor, but theformer captain's motives and objectives may not be as clear cutas he's lead her to believe; and more is revealed aboutIrving's return to the world of the living.
