This was odd and unique.
It deals with parallel universe theory, set in Croatia 1945, towards the end of WW2. MC Lina is working as a cartographer for a mysterious organization dealing with maps that correlate to the multi-verse. She's technically still in training, and about to embark on her first 'mission' as it were. But how that comes about, is very poorly framed, and a bit unbelievable, to me. That her very first solo mission going off-world wouldn't be assisted more by her mentor, or the person she is going to meet vetted far more thoroughly.
What we find out is, Lina wasn't expecting to come face to face with another version of herself. It goes against all the rules for them to even meet, let alone get involved in each others lives, or alternate worlds, but Karol and her butch dapper energy has Lina going crazy, right from the get go. And the feeling is mutual.
This is where it got kinda odd for me. It was strange to think about two women who are in many ways identical, as twins - and a ruse they utilize - but yet are different in style and body. Lina being very femme, curls, dresses, makeup, stockings - the whole 40's femme bombshell. While Karol has short hair, wears suits, and has tattoos and working class swagger and musculature hiding underneath.
It does that thing I hate in romance, where panties are soaking just from basic looks, and I really do have to wonder if that's something that happens IRL. But despite that, the whole idea of being attracted to yourself brought up some weirdness, which was barely touched on, or discussed. Then once they do really 'go' there it has a few BDSM elements, arm/hand pinning, biting to draw blood, leaving marks, which never does make me feel comfortable. But just added to the overall weirdness and un-comfortability of the situation.
There's supposed to be a murder mystery going about, that is why Karol wanted to recruit Lina in the first place, to find out what happened to a rather eccentric friend and former colleague. Yet we never really get enough information to string together clues, and I very much felt the mystery could have easily been solved by Karol on her own, (or with help of her many "Friends" ex lovers etc) so it made little sense that she actually *needed* Lina, in any way for this strange 'quest'.
So the utilization of sci-fi elements was thin, at best. Basically the plot felt flimsy, utilizing the multiverse simply sex-play and doppelgänger banging, and not much real story overall aside.