That's tricky. I usually find that ideas spring from interests. I love history and it's a very rich crop to harvest. 'These Vile Guns' sprang from my wish to write about a strong woman. Margaret of Anjou came to mind and the disorderly period in which she lived was an ideal backdrop. I was always interested in firearms and this was a critical period in the development of artillery. My next book is set in the same period and will feature most of the original characters. I have had flattering requests from readers who want to know more about them.