Wrong Heir, Right Her

Madeline was already a well known lawyer when she went to a masquerade ball six years ago and spent a night with a man whose face she never saw. The man was Nicholas, heir to a large fortune. Madeline had the baby, a girl named Isla, and raised her without ever learning the father's name. Her half-sister Vivienne got hold of the keepsakes from that night and used them to present herself to Nicholas as the woman he had been looking for, which is how she got near the money and the family name. Madeline takes a position at Nicholas's group years later and is in the same building as him again. People inside the company work against her, some of it professional and some of it not, and there are threats that go past office politics. She and Nicholas keep ending up on the same problems. Isla has a rare inherited illness, and she has a birthmark that matches one on Nicholas. Both facts point somewhere Vivienne cannot argue with, and her account of that night stops holding together.