Since everyone loves a mystery solved, here's the answer to mine:
Damn kids!
We found the check last night. This is what happened: While we were gone last week to SoWal, Philippa had instructions to bring in the mail and lay it on the kitchen table. She's 100% reliable.
Her brother, however, is not. Alex drove home from college last weekend, arrived as the mail was being delivered, and took the rubber-banded bundle from the mailman. And promptly walked in the house, down the steps to the basement beer fridge (yes DestinDreamin, tell Mr. DD the beer fridge has been resurrected from the dead ;-) ), put the bundle down, grabbed a beer...and promptly forgot to bring the mail back upstairs to its designated spot.
We didn't know he came home that weekend and we haven't been downstairs either, because Philippa had a sleepover with all her girlfriends and didn't straighten out afterwards. As a point of principal, we stayed upstairs until she cleaned up downstairs.
See what a little housekeeping can do? Straightened out the downstairs, and voila! One bundle of missing mail containing not only the missing check but an adorable mermaid letter from Jdarg's even more adorable daughter.
Young college student is coming home
this weekend and is going to get a mouthful of abuse from his mama.