The Chronivac had a small radius so they could only make changes to a person and surroundings when they were close. Altering other people's awareness of the changes was merely an illusion strictly associated with the changed individual, meaning that there was no true reality change for anyone except the target of the device.
Of course, this was optional, meaning that the user could set awareness of changes on or off at any time and could even set the affected persons awareness of their own changes on or off. Our couple would make it so every subject knew what they were going through though, otherwise what fun would it be?
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After checking their list of debtors, Mary saw the perfect test subject. He was Albert, a conservative catholic priest who came to them in despair to get money to keep his church afloat, as his village was getting less and less people willing or able to give donations. He wanted to keep the church running for all the elderly people who still attended mass. He truly lived by the Bible.
He wouldn't be missed by anyone since people would just assume he was forced to close the church and he spent so much time worrying about his situation that he didn't have connections outside of those elderly people.
Mary had the perfect plan for him. First, they created a basement under their house which was going to be a dungeon to keep their subjects.
They added one cage to it, they could always expand the room to fit more people, besides, this was a temporary solution since they just wanted to experiment with the Chronivac as soon as possible on someone. As they worked on the dungeon to make it have an unsettling atmosphere,
Mary told John about her plans for Albert. John loved the idea and so they finished with the dungeon and got in their car, headed to Albert's church.