Can You Solve This Mystery?

Okay readers, I have a challenge for you:

In the wee hours of Thursday morning, September 8, Skippy and Peaches, while on their way to the airport, noticed a shoe in the front yard. It was not one of their shoes, nor did they recognize it as a shoe belonging to Hubby or me. They left it in the yard.

On the afternoon of Monday, September 12, upon returning from Colorado, I, too, noticed a men's brown shoe in our front yard. I was tired and didn't bother to pick it up.

Today, September 18, Hubby went out to mow the grass. The men's shoe was still there.  It's a very nice men's shoe, and Merell brand, in very good condition, men's size 10.5,  (It's Hubby's size and he would like the mate because again, it's a very nice shoe.)

So here's the mystery, all you budding mystery writers:

Whose shoe is it?  How did it get on my front lawn?  Where is the mate? And, are the people who lost it coming back to get it?

I'd love to know what you think!

And as for why we allowed a random shoe to sit in our front yard for more than 10 days, I have no real reason.  We're not outdoorsy.  Not even a little.