I'm about 100% sure I saw the TV movie version of this book when I was around 7 or 8 (I'm sure my parents didn't know about it), and it spooked the junk out of me. I have vague flashback memories of Bette Davis in some sort of frilly bonnet and of a small boy in a sailor suit on a tricycle and some little girl screaming, and when I started to read this book, I realized that those memories were from this story.
Tryon does a really great job of amping up the dread factor without making the reader frustrated by the slow pace of the story. In fact, I actually found myself enjoying the drawn-out plot and didn't want to race through to the end, which is rare for me.
The story follows a young(ish) family of three who moves to a small New England town from New York City to give their marriage a second chance. They're initially charmed by the quaintness of the homes and residents, but it isn't long before the husband begins to notice that things are beginning to get undeniably weird. Of course, he's the only one who seems to care.
I don't know what it was about the 70s, but they always seemed to nail the whole creepy genre. Maybe they were all just horrified by their clothing and hairstyles and it seeped into their writing.