Not only all dresses fit Leti, there's also an L monogrammed on her towel when she exits the bathroom.
The book uncle George tilts to open the secret bookcase-door is"The House On The Borderland". This very influential 1908 horror novel moved the genre from the 19th century gothic style into what we now recognize. It was H.P. Lovecraft's main inspiration for his own style.
When Atticus, Leti, and George sit for lunch at the Braithwhite Estate, one of the dishes is octopus tentacles, a morbid nod to the shoggoth mouths.
The episode won an Emmy Award for Outstanding Guest Actor in a Drama Series - Courtney B. Vance for playing George Freeman.