Diamonds, Drama, and a Dash of Destiny (Shivian-The Nursery Nurse)

What will unfold at the Halloween ball? Who is Vivian really, and will she disrupt the wedding? Siobhan is torn: why can't she leave Robert, and what makes her want to? Join me, as I explore these tangled relationships and possibilities. I have a few theories...
Focus is Siobhan/Vivian, but the other couples either get a mention or an appearance. Also, heavy Mialotte as sidekicks. (Cross posted to Ao3)