Monstrous Nights is the second instalment on the dark fantasy series The Witch's Compendium to Monsters, written by Genoveva Dimova, published by Tor. An excellent sequel to Foul Days which plays with the world and the consequences of the changes that already happened in the prequel, two cities that are suffering the shock of two cultures merging after the Wall fall, and in the middle of all, our two characters, Kosara and Asen, six months later.

Kosara has returned to her position in Chernograd, after defeating the Zmey, and with her twelve shadows; but the memories of her story with the Zmey are still haunting her. A witch with two shadows appeared dead, monsters are being sighted outside of the Foul Days and Kosara sees cracks in the sky; the barrier between worlds is breaking and Kosara will have to repair it before the monsters invade this world.
Asen continues chasing the last lead in a case of several witches murdered, against the orders of his superior and the mayor; he's convinced that Karainov is involved, and his investigation takes him back to Chernograd, where his path will eventually get interwoven with Kosara's one, restarting the relationship between both while they try to save the cities from the monsters that are threatening their unaware citizens.

While the plot takes a bit more to pick than in the prequel, I personally enjoyed how much growth there's in everything shown in Monstrous Nights: from the cities that are experiencing a cultural shock, with a certain rise of xenofobia and extremism, the own characters, and even the own mythology, as more details about the Zmey and the monsters are explained. The relationship between Kosara and Asen is delicious, even if they get angry sometimes because both are strong characters, but eventually you almost get a cozy feeling from this book (if you ignore the murders, the monsters and the darkness, there's space for laugh and heartwarming moments).

Both cities have changed after what happened during Foul Days, and we can see how greed is also driving the actions of some of the characters, aiming to restore the Wall and keep both cities separated. More monsters inspired in Slavic folklore appear, but Dimova also makes an excellent job of humanizing some of the creatures, going far from the mindless beast idea; in general, Monstrous Nights is more, all built on the foundations of Foul Days. 

I loved each single page on the whole duology; if you are looking for a Slavic inspired dark fantasy that also drinks of its story, The Witch's Compendium to Monsters is the perfect election for you. Monstrous Nights is the culmination it needed, but personally, I would love returning to Chernograd at some point!