The Woman in White became terminally ill and needed to find a cure quickly to survive for much longer. She was permanently linked to her twin brother by both blood and super power. They shared a ‘Dual Intangibility’ which meant that only one of them could exist in full physical form at a time. Her brother was even more desperate than she, as he did not know what would become of him if the Woman in White were to die.
They both attempted to do good with their extraordinary power, fighting crime at a low level with some success before she became ill. Red Mist had noticed their crime fighting efforts and offered a potential way to help them. The Woman in White has approached this offer with some trepidation. They had never worked for anyone but themselves before and she wondered what the catch might be. Her brother was less inclined to ask questions and tried hard to convince her to do it.
Dual Intangibility gives both brother and sister a sizable advantage in any fight as it is not simply a 2 versus 1 situation but also an opportunity to pick and choose when and where to get their moves in by working together.