Gosh, I liked this quite a lot! The sense of time and place was really beautifully done, the plot and characters were rock-solid, the motivations behind why people entangled themselves in these enigmatic bargains were believable, and the romance was romantic. 

However, I'm not entirely sure we ever learned what Clara's trick was. Was it that she had to enable agreements for others, as she was doing at the beginning of the book? Rough if so. But that wasn't fully clear. Also, as extremely hawt as Israel was, I'm not sure that 'you're the only person who doesn't view me through the lens of my magical burden' is a strong ground for a relationship. 

And cameos from historical figures, like Langston Hughes, always feel a bit forced. The bit with W. E. B. Dubois was handled better.