Grant sure did love his seasons. I think every story of his that I've read thus far start out talking about what season it is. This is useful from a setting standpoint, but then he goes on and talks about how the season is ominous and portentous. Again, that's pretty useful for a horror story, but it's interesting to note that he does this in nearly every story he writes. If he doesn't start the story with a season, he uses a sudden change in seasons as a method of signalling a change in the tone of the story.
He also loved using wind as a threat in his stories. That was most apparent in The Bloodwind, but it's also true of Night Songs and now The Tea Party, as far as recent reads go. He might have used wind more often that that, but those are the ones I at least recall off the top of my head.
This isn't to say that framing his stories in a season doesn't work; it lends atmosphere to the stories, as anyone who's read The Halloween Tree or Something Wicked This Way Comes can tell you. Also, sudden, inexplicable changes in weather are a good way to indicate something's not right without having to show us ghosts, ghouls, and goblins to prove it to us. Since Grant's style is gentler and quieter than what most readers expect of horror fiction, these conventions work in his stories. One of the problems with this book is that the atmosphere is introduced at the beginning of the story, and then revisited too infrequently.
Overall, The Tea Party just isn't that great of a book. Part haunted house story, part Invasion of the Body Snatchers, the book has too many characters, too many subplots, and just isn't that engaging. The real threat of the story here is -- wait for it -- rocks. Boulders, stone buildings, and gravel all play a part in the threat, but the real antagonist here is a bunch of rocks. In a moment of clarity not often seen in Grant's works, he provides a background for the threat and why it is, of all things, rocks, but it's still hard to get past the fact that it's something mundane. Bentley Little might be able to get away with something like that, but here it's just laughable.
While the title of the book isn't inappropriate (a tea party does, in fact, feature past the halfway point of the novel), it is a little misleading. I kept expecting the tea party to be the source of the horror, and once it gets underway, it is a bit horrifying, but it wasn't like the tea was poisoned or anything like that. The book could have been called The Stone House and made more sense than The Tea Party and been a bit more relevant to what the story was actually about.
So far, what makes a Grant book a Grant book is his atmospheric style, and when it's absent from his books, they wind up feeling like just another horror novel. He did have some eerie, creepy moments, but where his previous novels were more about the feeling one got from the story, this was more about the events. It took a long time to get going, and then the conclusion happened quickly, too quickly to really feel anything for the characters who were affected by the tragedy.