I’m a fairly rational, left-brain person, but some things reason just can’t explain and one of them is writing. Where do ideas come from? Where do fictional characters come from? How do you find out where they live?

Most fiction writers I know will tell you how their characters direct and occasionally hijack their plots. I , the fairly rational, left-brain nonfiction writer, will tell you this. If non-writers talk like that, they risk being sedated or locked up or, if they’re Joan of Arc, burned at the stake.

What I write is limited by my experience. If I can’t imagine something, it doesn’t show up in my writing. But the stuff that I do know shows up in my writing in the weirdest ways. Sometimes I don’t know I know something till it appears in ink on the page before me.

Deena Churchill is a Squatters’ Speakeasy character. I didn’t know where she lived, but her son, Mark, and his band were about to show up at her house to practice so I had to figure it out PDQ. When Mark and his bandmates pulled into Deena’s driveway, what did they see?

A traditional cedar-shingled Cape with two 12-over-12 windows on either side of the front door. Cedar shingles and Cape Cod dwellings are ubiquitous on Martha’s Vineyard, so that was no surprise, but 12-over-12 windows?

At least one member of my writers’ group didn’t know what “12 over 12” meant, and a couple more thought 12-over-12 windows were rare, or found only in very old houses. So I wondered: Why did Deena’s house have four 12-over-12 windows in front?

Well, a house that Travvy and I walk by several times a week has 12-over-12 windows in the front, and on the side too, along with a 6-over-6 on the second floor.

House on Pine Hill, West Tisbury

On my next trip to the post office, I noticed that the West Tisbury branch of the Martha’s Vineyard Savings Bank — my bank — had 12-over-12s all around. It was built in the late 1990s and so doesn’t qualify as “old.”

M.V. Savings Bank, State Road, West Tisbury

So 12-over-12 windows had been scavenged by and composted in my writerly brain. What did my editorial, analytical left brain have to say about the windows on the front of Deena Churchill’s home? “Goddamn,” it said, “I’d hate to have to clean those buggers — but given Deena’s financial circumstances, it’s highly unlikely that she does her own cleaning. Let ’em stay.”

And stay they have. The interior of Deena’s house, it turned out, isn’t traditional at all. And every time I turn around, I see more 12-over-12 windows in my town.

Next door to Alley’s