I just recently read this paragraph: "Think of an ad campaign that you still remember long after viewing it. Consider a book that might have inspired you. Behind those memories are solid writing."
I would say grammatically, the subject of that bolded sentence is "writing," and "behind those memories" is a prepositional phrase modifying "writing." Therefore, the verb would be "is" not "are" since it needs to agree with the subject. (solid writing, which is singular).
But even if it were changed to "Behind those memories is solid writing," I still find the sentence awkward. I am trying to figure out how I would reword, but perhaps, I am wrong, and it is fine as is.