In the Dresden Files books, at some point Harry trades in his canvas duster for a leather duster? Which book did this happen in and why?
He was given it by Susan in preparation for the climactic battle in Fool Moon.
I stood up, but Susan grabbed my wrist. "Harry," she said. "Wait a minute." She knelt down by the bag and drew out a heavy box, flat and broad. "I was going to give it to you for your birthday. But I thought you could use it."
I tilted my head and took the box in hand. It was heavy. "What is it?" I asked her.
"Just open it, dummy," she answered, smiling up at me. I did, and inside was the smell of soft, worked leather, sensuous and thick, wrapped up in translucent paper. I tossed the lid aside, took the paper off, and found dark leather, new and matte black, hardly casting back the light. I took it out of the box, and it unfolded into a heavy, long coat, like my own duster in design, even to the mantle around the shoulders and arms, but all made of the finer material.
Let me just add that he gets another leather jacket in Cold Days, right before the climactic series of battles. This time he's given it by Molly.
Who, um ... sort of stole the money from White Court vampires to buy it