Baltimore is Smalltimore; you can’t keep a secret in this town. So, in that tradition, I will jump right in and reveal the surprise that awaits those who gather this weekend for the 14th annual Harvest Fest in Reservoir Hill.

The main event is the neighborhood’s celebration of the brilliant mural that Shawn James conceived and painted on the side of a rowhouse with the assistance of fellow artist Brian O’Rourke. It’s a real eye-catcher, mixing reality with mildly abstract imagery: Big black-eyed Susans and purple coneflowers, and hands holding a clear glass jar with three lightning bugs inside.

The jar is ajar, the bugs about to flee.

In a city adorned with an abundance of great murals, James’ “Lightning in a Jar” is one of the finest I’ve seen.

It hollers with life and provides a splashy, welcoming backdrop to a fenced community garden at Linden Avenue and Whitelock Street.

The garden is new, developed over the summer on a grass lot that had been known to attract fireflies.

Visitors will see flowering plants native to Maryland each year, making James’ mural nicely representative of the garden.

Now, as if the tall tableau were not enough to delight the eye, here’s Shawn James, at the garden gate, to tell us about the surprise:

“So there’ll be signs here that are going to explain the mural and have a QR code. You bring up your phone and you click the QR code and it takes you to an app. Once you hit the app, you hold your phone up to the mural so you can see the mural through your camera lens, and then this superimposed animation comes on.

The hands will hold the jar, the flowers bloom. You tap the screen and the hands unscrew the jar. It becomes nighttime and the lightning bugs fly out of the jar and they light up.”

At this, I had to cut James off.

“Stop right there,” I said.

I got a little too excited and needed a moment to grasp the concept: This mural, this tableau in Reservoir Hill, will be transformed into some kind of digital tableau vivant.

The technical term is “augmented reality,” and James arranged for it through a company in Detroit called Brand XR. The technology combines reality, in this case the lightning bug mural, with overlay images that make the thing come to life.

I got a sneak peak at what it might look like, and all I can say is: Way too cool.

“I’m not the pioneer of applying [augmented reality] to murals by any means,” says James. But neither he nor I knew of a digitally animated mural anywhere in Baltimore. So this could be a first for the city.

And it’s because the Reservoir Hill Improvement Council — Kate Jennings, executive director — wanted “something that’s kind of fantastic” from the commissioned mural.

Glow-in-the-dark paint for the lightning bugs was one idea, but that proved technically difficult and probably not sustainable.

“But Kate was adamant that she wanted something different,” says James, who trades as Mural Masters and has by now painted more than 200 murals, exterior and interior, near and far, public and private.

He’s a long-timer in the public art world, a former Open Society Institute fellow and, for five years, head of the city’s mural program.

He established Mural Masters about 14 years ago. There have been a lot of technical advances in muralism in that time.

“I did some research and I started looking into augmented reality,” James says. “I talked to a guy that I met in Detroit [at Brand XR], and he and I were talking about how we can make this thing go to the next level. He showed me some stuff that he’d worked on before with other clients, and I’m like, ‘Yeah, let’s do this.’”

I sense the start of something cool, with murals elsewhere in the city coming with a QR code and augmented reality.

Consider the Chesapeake-themed mural that James and Charles Lawrence painted in 2016, at Fayette Street and Milton Avenue, north of Patterson Park.

It would be thrilling to see the big rockfish in that tableau eat the yellow perch it appears to be chasing.

If you want to be among the first to see “Lightning in a Jar” come to virtual life, the Harvest Fest is Sunday, from 11 a.m. until 3 p.m., in the 900 block of Whitelock Street, with the mural’s dedication ceremony at 1:30 pm. Bring your phones.