Yes, these are YA novels (actually, they were YA back in the 1970's which means they're probably more for children these days!), but when I read them as a child -- the images of Lewis Barnavelt being followed mysteriously by some cloaked figure, as well as Rose Rita Pottinger driving a car to look in the rear-view mirror and see a pair of yellow glowing eyes -- SCARY!!!
Something Wicked This Way Comes
Comments on The Figure In the Shadows and The Letter, the Witch, and the Ring from Nicole: