Thompson, 53, went to the store to pick up a pair of $3.99 jean capris her daughter suggested she might like because of all the "bling" on them.
But when she returned home to try them on, she discovered way more "bling" than she had bargained for. There was a diamond ring in the right pocket.
"I took the ring out of my pocket and I sat on the floor with my daughter and her fiancé. I put my arm out in the center, and I opened it in my palm and we all just went, 'Wow. Oh my God," Thompson told ABC News.
All Thompson could think to herself was, "Oh geez, somebody lost their ring. The husband or fiancé must be out there saying, 'You're not getting another one!'"
Now Thompson, of Ham Lake, Minn., is working with Goodwill to try to find the ring's original owner. They posted Thompson's unusual "Lost and Found" story on their Facebook page in hopes the owner will see it, come forward and claim what's rightfully his or hers.
As of 3 p.m. Wednesday, she said Goodwill had received about seven emails from people claiming to be the owner, but there was nothing concrete.
Thompson is leaving the background-checking up to Goodwill. She did, however, have a very specific way she'd like the scenario to end.
"This is how I see this whole story ending: Somebody comes forward, says they lost the ring, says they're insured and have the papers to prove it. That's how I'm hoping this ends. So far, it's not that way, but we'll see. Only time will tell," said Thompson.
When she first found the ring, Thompson contacted the local ABC affiliate in an attempt to find the owner. The affiliate covered her story and took her to a jeweler to have the ring appraised.
Not only was the diamond ring real, it was worth $6,500.
"They gave me an estimate on how much it was worth, and that was another 'whoa' moment. How long do I have until it's mine," she laughed.
For now, it seems to be "finder's keepers." But Thompson ideally would like to see the ring safely returned to the right finger.
"I need to find the owner, and I'd love to hear the story of how it got in there," Thompson told KSTP News.
If you have more information, Thompson urges you to visit the Goodwill Easter Seals Facebook pageand send a message. LINK