Ann Templeton is an adult in the books. She is described as stunningly beautiful, looking exactly like Madeline Templeton, her ancestor. In the books, she often plays an antagonistic role, but had helped the team from time to time.
The Secret Path is extremely significant in the books, as it is apparently the reason for the town being strange. Both an inter-dimensional gateway and a time portal, it can only be opened by visiting a set of places in sequence. In the series, the path acts just like some sort of time window and, apparently due to budget constraints, it is never featured again.