"You know so little of war. Battles may be fought from the outside in, but wars are won from the inside out."

There are four parallel worlds, each with a different take on magic and a city named London as its center. There is magicless Grey London, Red London where people believe in a balance between people and magic, White London, where people are draining magic in order to control it, and once, there was Black London. Kell is one of the last magicians that has the ability to travel through the worlds and maintain communication between them. The doors between those worlds used to be open, but when dark magic started to destroy Black London, other cities started to close their borders in order to stop darkness from leaking. That was 300 years ago, and no one has heard of Black London since then. 

Despite the fact that I usually don't like concepts of parallel universes/multiple dimensions, Schwab's worldbuilding was refreshing and fun. There was no infinite number of universes because I hate when authors pull out a bunch of worlds with same people, just some details in their paths made them different. No, this felt like a book, with four pages that are independent but connected in a way. The worldbuilding and development of the story intertwined with amazing writing made this book easy to read while simultaneously adding just enough new information to keep story flowing and maintaining a sweet dose of mystery. 

Another interesting concept in this world is magic. I don't think I've ever come across such an original way to introduce magic. In author's vision of this world, magic is everywhere and in everything. It is a living force, and some people have more affinity, some less. Those four worlds are lined, Black London first and closest to "the source of magic", then White, Red, and Grey the farthest. In Red London, people believe in equality between magic and its users (Kell described his use of magic as a conversation between them), there it is worshipped to the point of it being a religion. Grey, being the farthest from the magic source, has used its supply of magic and it no longer exists there. In Black London, people let magic take control in order to gain power until it started to control and poison them. Seeing that, people of White London considered the only way of using magic is by controlling IT and being its master, so in their world magic started to pull back, and that world, too, is starting to die. It was really interesting to read about such different insights in magic and power and how it affects people and worlds. It was so well written, developed and described that I found myself thinking about correlations and consequences of human behavior over and over again.
Although the plot wasn't at peak of the action at all times, story was always entertaining. Schwab has a simple way of maintaining the intensity, if not by action scenes, then by following the character development or some other factor, in a manner that keeps story flowing and interesting. Whenever there wasn't something super interesting or intense going on, I was like "uh this is going to be boring", but it actually wasn't disinteresting, just slower. That is in fact why I liked the writing style so much: the author has written this book with perfect timing. She knows just when to speed up or slow down the course of action – it is always intriguing, but understandable and well thought through.

Story is told from a third-person perspective of two characters, Lila and Kell. I liked those two, but I didn't really love them. (I am writing this review after reading first two books and in the second one they were absolutely amazing and I would die for them, but in the first book they were not so cool xd). They were cool and I liked that author didn't give them any basic, cliché characteristic, like a hot troubled dick who is actually good underneath or beautiful shy girl that doesn't know it. Nope, Delilah Bard is 19, thief and cutthroat and learned to survive on streets of Grey London on her own. 

She hated commitment and caring because she fears it can only be used against her. From time to time I found her annoying because she always throws herself in danger and wants "adventure", she is quite selfish, but aren't we all. Anyway, she is pretty badass and cool, always prefers black man's clothing and a good set of knives, and important! Was never described as pretty (why do all heroines have to be pretty).

Kell, although seems ordinary, has a lot going on. He is a member of the royal family that rules Red London. Just a member, since they adopted him, for he is one of the two remaining magicians who can travel between worlds. Kell has everything he can wish for – wealth, love of king and queen and his best friend (and crown prince) Rhy. But still, he feels like a possession, just a symbol to show other empires the strength of Arnes. I like his character and there is a lot about his past to be discovered and I think he can only get more interesting (he did, ha!).

Relationship between Kell and Lila was developed in a not-so-romantic-but-still-cute way, they both don't know what they feel, and tbh they don't feel anything towards each other until the end of the book. There are no love triangles, drama or something forbidden, it's just… complicated. *spoiler* that ending when Lila left was exactly what I needed. 

As I said before, I already read the second book and it is really good. If you have doubts about continuing or starting these series, I wholeheartedly recommend them to anyone with a fondness for magic or adventure.