Cas Russell

Cas Russell is crazy good at math. She can calculate vectors and probabilities to get her out of almost any hot spot, but in between jobs it overwhelms her, showing her the mathematics of every aspect of anything she looks at and every movement she makes. Her one steady friend-not-friend is Rio, but lately she's been learning that she can have other friends as well. She's also beginning to learn some unsettling things about her past and why she might have these uncanny calculation skills in the first place.

History
This is a mystery slowly revealed over the course of the series.

Friends & Associates
At the beginning of Zero Sum Game, Cas doesn't have any friends. The closest thing she has to a friend is Rio. Over the course of the series she begins to fumble her way through having real friendships.

Rio
Rio fulfills all the requirements of friendship except for actually caring about her.

Friends
This is new for Cas. She isn't very good at it.

Checker
Checker drinks with her in between jobs, and made her watch the Star Wars Holiday Special, for which she will never forgive him. She figures she shouldn't let him get killed, though.

Arthur
Cas has this weird desire to keep Arthur from dying. He also has this annoying habit of being her conscience.

Pilar
Cas offers to shoot people for Pilar and Pilar breaks into Cas's apartment to clean up vomit. That makes them friends, right?

Sonya
They work well together on math, but their personalities are different to say the least, and Sonya reminds Cas of a painful hole in her life.

Malcolm
They meet when he shoots her.

Clients
Clients are not always friends.

Dawna
She never pays her fee.

Noah Warren
He wants his daughter back.

Reluctant Allies
These people are usually unfriendly towards Cas, and she towards them.

Unnamed Anti-Pithica Organization
This includes the persons known as Steve and Finch.

The Lorenzos
After they stop trying to kill her, before they start trying to stop all her business.

Agent Jones
Might be classifiable as an antagonist as well.

Reuben McCabe
Right-wing radio host

Antagonists
Antagonists are not always enemies, and sometimes the biggest problem is Cas herself.

Organizations
Pithica

They want to make the world a better place.

The Lorenzos
Honor must be served.

Arkacite Technologies
Before she tries to save them.

DHS
Also sort of an ally, at different points.

Dawna
After she's a client.

The Lancer
Obsessed with solving P vs NP.

Jacob Poudry
Human trafficker and piece of shit in the first degree.

Other
At the end of Zero Sum Game, Dawna rips through some careful telepathic word in Cas's mind. As the series unfolds, Cas begins to have more and more problems with her brain.

Jobs
Retrieval jobs that Cas is hired for or agrees to do. Non-retrieval jobs that Cas is roped into doing by herself, friends, or clients:
 * Courtney Polk
 * Courtney Polk's US life
 * Samples for Harrington
 * Liliana
 * Gemstones
 * Math proof and thief, and creator
 * Trafficked children
 * Stop Pithica
 * Murder rehab
 * Help Checker with Mama Lorenzo
 * Quell robot and anti-robot violence
 * Be a better person
 * Take down Poudry
 * Stop widespread crime in LA

Pithica
This starts in Zero Sum Game and continues in Null Set, although the presence is felt throughout the intervening books.

Cas Russell's Past
At first she doesn't realize it's normal for other people to have one. This arc includes the role of Rio in her life.

Friendship
Friends are hard.