But now I think I always knew there would be consequences to Lexie Madison.
-- Narrator (Chapter 1)

Importance: Cassie admits that even when she and Frank created Lexie, she suspected that she would not be able to totally abandon that persona. Still, she was shocked to learn that a woman had stolen that identity and was living as Lexie.

This girl is my double, Sam. This girl was going around wearing my fucking face. How do you know your guy got the right one?
-- Cassie (Chapter 2)

Importance: When Sam argues that Cassie does not need to get involved with Frank and the undercover operation, she points out that she and Lexie look alike. She suggests that perhaps the killer was looking for Cassie and killed Lexie thinking she was Cassie.

But maybe it goes some way towards explaining why I said yes to Operation Mirror, and why, when I signed on, I figured there was a decent...
-- Narrator (Chapter 3)