The high concept is that Helen has a particular special ability of Brain Transplant. Given a pair of willing (or subdued and unconscious) victims, she can in ten minutes switch their brains. (Yes, this could only happen one-way, but that would be unethical!) Othar has explained to her that this world is groaning under the tyranny of the Wulfenbachs, and she has agreed that the most logical way to deal with this is to switch his brain with that of Klaus, or at least Gil -- then he can bring down the tyrants using their own powers against them.
Meanwhile, this plot is being supported by several others. Beetle is helping out, because he believes Klaus to be in some fashion deeply evil. (Not clear in what way, but it's clearly mistaken.) Silas is doing so out of sheer revenge, and he would like to figure out how to be the one who gets transferred instead of Othar, so he can take over. Moloch wants a bit of revenge, but mostly is helping out because Othar is his ally, and he would be content to have an ally in charge of things. Theo is not in on it -- while Othar wants to bring him in, Moloch convinced him that Theo wouldn't think well of it, and he's right. Theo is suspicious that there is something going on against Gil, and he is worried about that: while they may not be exactly on the same sides, they are old friends, and he doesn't want Gil hurt.
Darker: If two brains are switched, how is this handled from a gameplay standpoint? "Swap name badges" seems faintly unsatisfying, but "swap characters" seems actively problematic for a great many reasons.
Justin: I'm thinking of this as effectively a disguise mechanic. I agree that it's not as satisfying as one would wish from a metagame POV, but it's what makes sense from a game-goals POV. That is, the point of doing a brain swap is precisely that these characters are now wearing each others' bodies. (And no, they don't learn anything about each other in the process -- this is very explicit in the Narbonic source material the mechanic is drawn from.) One implicit assumption that I probably haven't stated explicitly, which is relevant: game badges are pictures, not text. I'm planning on buying a button-maker, and giving everyone a badge that shows what they look like, rather than what their name is. (That's why I've been noting good pictures for everyone in the notes.) That makes the brain-swap at least slightly more visceral.
As part of this plot, Helen is deliberately flirting with Othar to manipulate him. She isn't really particularly attracted to him, but she does know how to use feminine wiles. And heroes are so much fun to manipulate!
Characters In Game: Beetle Gil Helen Moloch Othar Silas Theo
All Characters: Beetle Gil Helen Moloch Othar Silas Theo