Nightstrider is the first book in the eponymous dark fantasy series, written by Sophia Slade (which represents her traditional debut), and published by Orbit Books. An ambitious and fast-paced story where nightmares and human will have to ally to stop the conquest of both worlds, waking and dream one, by Para Warwick, a vicious demon which is one of the few night creatures with the ability of jumping between realms, told using several POV and that includes a great layer of romance.

Wren is a nightmare, bound to Para Warwick; when she fails to retrieve information about a weapon that might be used to end Warwick's realm, she's severely punished. After losing the grace from Para Warwick, she decides to aid the growing rebellion in finding it; there, she gets to know Alaric, another nightmare that is trying to get redemption for his past actions. Despite they are initially wary of each other, they decide to collaborate if that means taking down Para Warwick and liberating Wren from the bond that ties her to the Para.
In the waking world, Prince Caine, Warwick's human son, is preparing to wed Ila Enovoldson, queen of a neighbouring kingdom; a step to cement Warwick's ambitions of conquest in this plance. But Ila is also a Weaver, a protector of the Boundary that separates the waking world from the Reverie (the dream one), and she has accepted this agreement as the mean to retrieve a weapon that was trusted to her; when Caine finds her opening a portal to the Reverie, he will follow her, finding himself in a world where his father is even more monstrous. Their paths will collide with the one of the two nightmares, and they will need to collaborate to stop Para Warwick and preserve the Boundary between the planes.

We are gradually introduced to the four POV, slowly weaving the plot together; four characters that are splendidly developed, and that evolve through the whole story: from the Wren that started her journey just as a means to get revenge to the Alaric that hoped for something better and to wash away his sins; the innocent Caine that cuts the cords used by Warwick to control him, and Ila, probably my favourite one, a strong female character that will sacrifice herself if that means saving the rest. 
The Para himself is an excellent villain, ambitious, but with his own secrets; a creature that craves for the control of both worlds.

The worldbuilding is at the level of the best epic fantasy, with the two mirror worlds and a unique magic system, based on those manifestations formed on the dreams; Slade doesn't give us much information at the start, choosing to show partial pictures of it, in consonance with how her characters start.
The story is relatively fast-paced, avoiding slow moments; smartly playing with the different points of view, in a way that not many novelists could do it. The romance will be delightful for those that prefer slow burn and enemies to lovers as their mojo.

Nightstrider is an excellent debut novel, one that I recommend if you like multi-POVs high fantasy stories but with its own dash of uniqueness. Sophia Slade is a voice to watch, and honestly, I can't wait to continue reading the Nightstrider series.