She is only allowed to fly to her destination, not anywhere else. She notices that she is not where she should be, that she cannot progress to where she was told to go, and she careens out of control when her wings won't flap anymore, and she crashes.
Time passes. Sherlock presumably sleeps. But when Promise comes back she will find him drinking tea again.
"If I ever have to introduce you to a fairy and you haven't picked a nickname yet I will call you Tea."
"I'm going to make a gate to another continent so I can plant my tree branch there and get food for myself," she says. "Where do you want this one? I can just put it right in front of the other if you like."
"Reasonable enough. Possibly tricky for anyone trying to go through one of them from this side."
"I wonder if you can reach through the gate into my tree if I don't actually say in words that you may."
"It shouldn't be possible according to the usual operating parameters of vampires. Who knows how the gate or the tree factor into it."
"My tree has a property that you can't get into it if I'm not meaning to let you, but meaning doesn't involve speech."
"Should I test it, then? One attempt to get into your tree never having been permitted by any means, one attempt having been permitted silently, and if that fails try a verbal invitation and if it succeeds try silently revoking permission? Permission for a vampire to enter one's home cannot traditionally be revoked except by magical ritual."
"It's per home when the home is not a tree. Seems logical that it would be per tree when it is."
"So at least one of the possible obstacles is in effect."
The tree looks like an abandoned house. It hasn't accumulated much dust, because it has no air holes. It is lit by fairylights and has some shriveled-up fruit in the cupboards and what is probably a bookshelf hidden behind a layer of wood for some reason and, on top of the bookshelf, a bed.
"Giving permission worked tree-fashion, but revoking it worked vampire-fashion, which is to say not at all since you didn't nail any crosses to anything. Well, that's an interesting interaction."