Thanks to all for your comments.
My wife is 500 miles away with my daughter who's having our first grandchild tomorrow morning, so I'm winging it on my own. When I called her to tell her about the girls being attacked, she reminded me that she has seen possums at our trash cans in the not-very-late afternoon.
BUMMER. I dropped by the house and checked on the birds twice. So far, so good.
Interesting comment by a wildlife rehabber friend who specializes in possum rehabbing. (I know. Don't even say it. I know what you're thinking

) Anyway, I called her to give her a chance to come and trap the juvenile possum before I dispatch it when it comes back--if it comes back. She informed me that possums are nomadic and that they are constantly ranging looking for food. That probably explains why so many of them get run over (and I always thought they just like to eat tire rubber.
) She thinks this one may be in another area by now. Unfortunately, there are plenty of its brothers/sisters/cousins/aunts/uncles/etc/etc to take up the gauntlet that is being passed.
I have been informed by The Boss that tonight I must single-handedly closely examine every one of our pullets to be sure they get treatment if they have a scratch or bite on them. This for a bunch of birds that I've NEVER even held except to put them back in the coop last night.
(Anyone in our area is welcome to come by and watch the proceedings. Should be rich.
Any suggestions on how to hold a bird, inspect it THOROUGHLY (those were my instructions), and treat it--all in the dark of night??
I'm not sure if I'm cut out to be a chicken farmer, but those feathery creatures have wormed their way into my heart, so I guess I'll be doing my chicken vet-tech training tonight.