A locked door meant nothing to Castiel, of course. He wouldn't have even considered to check the door in the first place. He appears in a corner of the office, staring down at his brother with a feeling of... discomfort. Certainly none of them were in the best of states, but rarely had he seen his brother bothered by much, save for Jim Keats, who bothered even Castiel.
"House," he calls as way of greeting, frowning when the other doesn't even seem to notice his presence, which isn't possible. He steps closer, looming behind House's chair. His frown deepens, and finally, carefully, he reaches out to lay his forefingers on the other's shoulder. "House," he says again.
For just a moment, it's like House isn't there at all. Castiel feels the sudden absence jarring, when House's vessel is indeed before him, but just as it happened, his senses realign and House looks up at him, startled.