Bogg and Jeff land in colonial Massachusetts. Their arrival is witnessed by a local who has them arrested as witches. Benjamin Franklin's mother is also under accusation, and if she dies, history changes. Jeff uses the Omni to prevent him and Bogg from being burned at the stake, but that puts them a couple of centuries forward and right in the middle of a seance being attended by skeptic Harry Houdini. Witnessing the ""supernatural"" with his own eyes, Houdini starts believing in ghosts, further altering history. The Voyagers Omni out, but return when Jeff determines they must convince Houdini they aren't ghosts. He and Bogg end up saving Houdini from being rescued alive, and put that part of history back on track. They then return to Massachusetts with one of Houdini's mirror illusions. Using it, they show that there are no such thing as ghosts and witches: only mechanical trickery. That ends the witch trials, and history is restored.
