What sparks a story?

What is the spark that fires a novel? For me, it's often an event or a conversation or a newspaper article or a chance remark that causes me to think... Wouldn't that make a great starting point for my next story? And that was how The Case Against Fili Du Bois came into being. 

Fili, heroine of my novel, is abandoned by her mother in the grounds of a church. That abandonment becomes the thread that winds its way through the book and determines Fili's future - and the future of the family who adopt her into their home on a wine estate in the beautiful Franschhoek Valley. 

Yet what made me choose that particular beginning for my novel? 
Some years ago, I happened to be passing by a church in the southern Cape Peninsula. Mounted on the side wall of the building was a sign that said:
Baby drop off
Ages up to 3

Clearly, it was an advertisement for a free creche run by the church to give young families some respite from full-time parenting duties, a place to leave their babes for a hour or so. But it got me thinking...
What if a child was dropped off at the church - and never fetched?
Would she languish in an orphanage? Would she be adopted? What would happen if her adoptive parents then have a child of their own? 
And The Case Against Fili Du Bois was born. 

More next time...