In Death of a Nightingale, their third thriller starring Red Cross nurse Nina Borg, Danes Lene Kaaberbøl and Agnete Friis intertwine the contemporary story of a Ukrainian asylum seeker—and murder suspect—on the lam in Copenhagen with that of two young sisters starving in Stalinist Russia.

What inspired Death of a Nightingale?

LK: There is a story about a young boy who was made a hero in the Stalin era for turning in his own father. There is a slight core of truth in it, but it was twisted out of all recognition by the propaganda machine.

AF: We found that intensely interesting, because, what would it be like to be a child and live in a society where you really couldn’t trust anyone—where the truth was always debatable?

What initially put Ukraine on your radar?

AF: Eastern Europe is intensely interesting to us Danes because politically it is very close to us now, geographically it is very close, and yet many of us have no idea what it looks like and what it’s like living there. It’s sort of like going into a parallel world where a lot of things are things we can recognize and then some things are just completely different. In a sense, it’s mirroring problems in your own society, so you can both see Denmark a little more clearly and you see another country as well.

How is the character of Nina evolving?

LK: Nina’s psychologically wired so that the only way that she can feel competent and in control is if she’s active, if she is the person saving lives or at least doing her best to rescue somebody from the ruins. So she’s not just a do-gooder, she also does it for herself in a way. Nina knows that what she does has caused her to become increasingly isolated from a normal life, from her family and from her children.

AF: Gradually our plan is to try to move her into a better place, because it’s getting unbearable for both her and us writing about it! We tried in the next book [the fourth], not because we don’t want her to care about other people any more, but because she needs to care a little bit about herself as well.

Do you see any thematic concerns connecting the series?

LK: There is definitely the theme of the outsider. There is a certain through-the-looking-glass theme where, on the one hand, you have the safe, everyday reality that most of us live in most of the time, and then right on the other side of that is a different reality that is much harsher.