There's a little free library on my street. A wooden box on a post, holds maybe ten books. Last month I left my favorite book in it — the copy with all my notes in the margins. 'This line got me.' 'Nobody recovers this fast.' 'I'd forgive him too.' Today it's back. Same coffee stain on page 41. But under every note of mine, someone wrote back in blue pen. Under 'I'd forgive him too' it says: 'You would? I've been arguing with you about this for a month.' I don't know this handwriting. I check the street. Empty.

I don't write anything. Not yet. I want to know who I'm talking to. I put the book back in the box, exactly how I found it. Then I set up on my porch with coffee and a clear view. Two joggers. A beagle. The mail carrier waves. 8:40 — someone in a blue jacket stops at the box. Takes out MY book. Flips straight to the margins. And frowns. Because I didn't write back.

I don't move. I just watch. Blue Jacket turns the pages slowly, standing right there on the sidewalk. Then they tuck the book under one arm and walk off — to the yellow house at the corner. The one with the wind chimes. Four years on this street and I've never once seen that door open. Now my book is inside that house. With no reply from me in it.

It takes me three days to get brave, and I do it with a pen. I buy a second copy of the same book and write on the first page: 'You have my copy. I have questions about your chapter 12 note. Coffee? I'm the porch with the white swing.' I leave it in the box facing the yellow house. Next morning, 8:40, my doorbell rings. Blue jacket. My book in one hand, the new copy in the other. 'You knew it was me?' Me: 'I hoped.' We've been trading margins ever since. Same street, one box, two pens.