It will be from Kate's POV. It starts in ep 09 in s 04 (Kill shot). Kate is still with Josh but they have lots of fights. And he maltreats her. He rapes her but she doesn't tell anyone. She loves Castle but Rick doesn't know it.
"I was listening to 'Sorry' by Halsey and it made me remember of season 4 of Castle. So I was thinking could u do a oneshot based on this music?" - prompt from @_stanaticlover_ on instagram, THANK YOU FOR THIS!!