"You can't have her."

He had made this deal to protect her. It was the only reason he was still working when he should have been long retired. It was why he kept bringing Castle back.

"It's her or your family."

Perhaps it should have been and easy choice. His wonderful, beautiful wife. His two precious baby girls. Or this…cop. Not a tough decision.

But then, Kate Beckett wasn't just a cop. He had trained her and watched her grow into the best detective he had ever seen. She was a co-worker, a teammate, a friend—somewhere between his daughter and his sister.

That's why it was hard. Because she was family too.

He would have given his life for any single one of them, so that's where he made his final stand: between his family and the world.