When I had the idea for Gentle Axe, to write a detective novel using Porfiry Petrovich from Crime and Punishment, that was the limit of my idea. I thought of it as a one-off. But my agent said it might be helpful to have some additional storylines up my sleeve as sometimes it helps to sell crime if the publishers can see the potential for a series. So I did. It went to Faber as a single manuscript, no mention of any other stories. But they got back to my agent and asked whether I would be interested in doing it as a series. I went in for a meeting and gave them the other storylines. The result was a two book deal. Obviously they were being relatively cautious in case the series didn't take off.