Available, for fiction or roleplaying, one historical plot bunny.
1797: James Tilly Matthews is locked up in Bedlam for interrupting debate in the House of Commons by yelling "TREASON" at Lord Liverpool, from the gallery. When examined, he explains that he HAD been involved in secret affairs of state, but that he was betrayed by Prime Minister William Pitt.
But the danger was what he'd uncovered on his earlier fact-finding and diplomatic mission to France. He'd gotten to know several of the anti-Monarchist Girondist politicians when he was there, which is presumably how he'd found out about the real danger -- the sinister "Air Loom", used by the French revolutionaries behind the Terror.
The "Air Loom" is an enormous piece of machinery, with kegs of various gasses containing psychoactive chemicals (the word didn't exist at the time, so I'm using it anachronistically, but it's the best description of what he was talking about). These gasses were derived from various noxious substances, ranging from bad breath to horse farts, but the point was that these psychoactive gasses were magnetically charged, then directed to blow at specific people.
And one was set up secretly in London. It could affect people in various theaters, coffee houses, and the like, places that these revolutionaries had infiltrated, and set up their contraption.
The magnetized gasses could have several effects. "Kiteing" was the basic one -- it was a way of implanting an obsessive thought into a person, one that just wouldn't go away no matter how hard the victim tried. A more subtle effect was "Thought-making", in which the victim's train of thought was simply sucked away and replaced with another that the Loom gang created.
And, indeed, the Air Loom could even be used for direct damage, through "Lobster-cracking", which was just as horrible as it sounded: by increasing the magnetism in the air around the victim, he could be literally crushed to death.
Images of a reproduction, and more historical information, are at this website. The Wikipedia entry on James Tilly MAtthews also has good information.
It is the first example of the kind of "Influencing Machine" Brooke Gladstone is talking about in her graphic novel about the media, which is where I heard of it.
So, there you are. A French-revolution era mad scientist mind control device, run by the secret society behind The Terror, and bent on destroying Great Britain by controlling her leaders. If THAT doesn't get your creative juices flowing, what would?