Thief breaks into a house in Oregon, cleans out the jewels, fences them for what he can get, the ring in question is sold to a pawn shop, a struggling young couple walks in and buys the ring, they marry, they move to the Midwest because of a job transfer, the wife dies, the guy decides to sell the ring on e-Bay, a woman in California recognizes her ring and buys it back.
That's the outline. Now what's needed is a Nicholas Sparks to turn it into a book, a movie, and a billion dollars.