The True State of Affairs
is a novella by Diana Wynne Jones.
Somehow Emily, from Kent, has found her way into Dalemark. Mistaken for a woman called Hilda, with whom she had swapped clothes, and captured in her place, she is locked away in a citadel with no prospect of release or escape. To keep herself sane she writes down her story and manages to use some of the paper for a secret correspondence with another prisoner who she starts to fall in love with.
The unnamed setting of the story resembles Dalemark, in much the same way that the setting of "Dragon Reserve, Home Eight" resembles a series of the Related Worlds.
The story was written in the 1960s, but did not appear in print until Everard's Ride in 1995. It was subsequently reprinted in Minor Arcana.