Kotlin in Action, by Dmitry Jemerov and Svetlana Isakova covers the language basics of Kotlin.
The book is supposed to be for experienced Java developers, but I have very limited Java experience and I was able to follow all of it.
I have to say I really like Kotlin, and how the language is made so that your code can be as short as possible. Even when your IDE can fill in most of the code for you, it is still a problem as you get tons of useless code to check all the time.
Overall, strongly recommended if you are interested in Kotlin.