I've been caught short more than once by a turkey that didn't defrost fast enough to be fully thawed by the time I was ready to cook it. I wasn't aware of it until now, but apparently there's a method to cook even a deep-frozen turkey without first defrosting it. San Francisco DJ Rick Stuart tells us how.
I just put the frozen turkey in a 325 oven on a lower rack in a rimmed baking sheet like you would use for cookies. That way hot air can get around it to cook. Don't use a roasting pan with high sides. Put a cup of water in the baking sheet. That's pretty much it.
About 2 hours in I pulled out the packet inside and everything else. I put some bbq rub inside and outside. I was tempted to put some cut onions and things like that inside the turkey but I think you need to keep it open as much as possible to get the hot oven air inside the bird.
I made sure all of it got to 165 especially down near the bones but not on the bone. The breast will overshoot but that was ok. Have a reliable and calibrated thermometer to check the internal temperatures. Don't use those silly pop up things.
Total cooking time was about 5 1/2 hours.
There's more at the link.
I presume that if you put the bird in an oven roasting bag, as I normally do when I roast a turkey, it will retain more moisture than if you just put it in "naked", with no covering. I won't need to cook from frozen this Thanksgiving (I hope!), but I'll keep this article in mind for future reference.
Mr. Stuart also provides helpful links to other articles on cooking a turkey, including one describing how to slow-cook it overnight at low temperatures. Very useful.