I was so sure I have never read this book, although many scenes were familiar. Turns out, I have the paper book, only the title in Spanish is completely different: "The Black Bracelet". And the original title in my book says "Kirkby's Changeling".
Good book, as expected. A Circus, a brave MC, hidden identities, kidnapping, attempted murders... it was a bit slow in some places, but overall, the adventure I was looking for.