As I circle to find a parking place, which is difficult in the Mission even on a Saturday afternoon, I notice an unmarked police car with a plainclothes driver keeping an eagle eye out for something. And a couple minutes later I see three cop cars come roaring up the street. They turn the corner by the cafe.

When I reach its front door I see the cops have detained two Latino teenagers dressed in the baggy, neutral uniform of the neighborhood: white t-shirts and black shorts. There are now five cop cars for these two kids, whom I had idly noticed walking quietly along a block away when I was looking for parking.

Inside the cafe, most of the tables are occupied with people studying or working on laptops. A young woman and young man are playing guitars — mostly ragtime and songs from the 1920s. They play a few choruses and then the woman sings one of those old songs in a clear tenor voice. (Their names, I found out when I looked at the CD they had for sale, are Craig Ventresco and Meredith Axelrod, and here’s a YoutTube video of them performing at the Atlas earlier this year.)

The cops let the two kids go and the police cars drive away. Almost no one in the cafe noticed the roust taking place across the street.

After several songs, the woman’s place is taken by a young man, who plays instrumentals while the woman passes a hat. Then a couple in their thirties — the man in a straw fedora, a woman in a sundress — stand up and begin to dance the tango. The guitarists are still playing ragtime but the dancers are good enough to do the tango to ragtime anyway.