Summary: Yvonne Hartman ignored what was truly important.
Yvonne Hartman was the worst kind of fool, consumed by an unquenchable hunger for more power. The return of the British Empire was her goal, no doubt with her right up there, if not in charge then whispering in the ear of the one who was. The sheer energy being produced by the interdimensional breach would secure Britain’s independence from the rest of the world.
As far as Hartman was concerned, the ghosts that started popping up everywhere weren’t salient, an unimportant side effect to be shrugged off and ignored.
Just like that, she came close to dooming the world.