Orlando has gone into hiding...somewhere in the subset of the house that is available to him. I last saw him Monday morning, when he was happy to eat canned food from (a dish in) my hand. He's around -- the food and water are being consumed and the litter boxes are being used -- but he's found a good spot and doesn't want to come out yet. Sigh.
There've been no feline hostilities that I'm aware of. These seems to be "new environment, scary!" anxiety.
I wonder if I need to postpone tomorrow night's vet appointment. How long does this phase usually last? (Giovanni seems to have skipped it, at least so far.)
Edit 11PM: Got him! The way to Orlando's heart is through his stomach; I used bowls of food behind closed doors to gradually narrow the search until I had it down to one room. Actually catching him in that room was a bit of a challenge, but he and Giovanni are now in my office together, where I plan to keep both of them until the vet appointment tomorrow night. After that they can have their freedom back.