Sarah Zellaby loves math, comic books, bad procedural dramas, and drinking hot ketchup mixed with orange juice and honey. And that's about where her dating profile goes off the rails (not that she dates, really; who wants to go out with a cryptid telepath who just looks like a cute geek girl?).
Sarah is a cuckoo.
She's never met her biological parents. They left her on the front porch of the Zellaby family of Cincinnati, Ohio when she was less than a week old, and the Zellabys took her in, believing that she was theirs. That's how cuckoos work. They leave their young in other nests, letting other people handle all the difficult, awkward parts of raising a child, and only come back when their precious babies inevitably turn on their human parents. There are very rarely survivors. Sadly for the Zellabys, they didn't survive; they were killed in a car crash when Sarah was still a little girl, leaving her to fend for herself.
She could have found a new human family. She could have found the cuckoos. Instead, she found Angela Baker, maybe the only non-homicidal cuckoo in the world, and her salvation.
Sarah grew up knowing that murder was wrong, which puts her well ahead of most of the cuckoos in her generation. She grew up with a family that loved her, no matter what she was, and with a strong sense of purpose.
Let's see how long that survives contact with the real world...and how long it takes for the cuckoos to come looking for their own.