43 Hidden in the clue, I'm not sure if you have any letters?
20 Hidden in the clue, with a slight jumbling. The spots are birthmarks, it's a word seen before in crosswords.
Thanks NAC.
I was looking at Wine and Vat individually. Taken together , easy to find spots.
For 43,I have ???ED?.
I have yet to solve 31d and 37d. I thought 43 will give me enough letters to solve those two.
I have the author and the two protagonists.
Have not found the eponym but the title of the book is obvius in the grid.
I will wait for the solution to see the colouring.
Thanks NAC and ProfessorM.
31d is Li(a Chinese measure approx 1/3 of a mile) and this multiplied by 10 would be approx 5km (I think) so it's LiTEN cycling around to give ENLiT.
The eponym is just the title of the book/series, which you have.
For the final shading etc take a look at what might suggest the country it's set in.