The writing on the wall
(Book)

"When Mary and her sister Betty visit the Ivy Bay lighthouse with their friend, Henry, Mary stumbles upon a crude map drawn on the wall. Henry wonders if it might be connected to his ancestor David, who was accused of stealing a large sum of money and a precious family heirloom. Mary decides to investigate, but solving a crime committed almost a century ago isn't easy, and a surprising number of people don't want her to succeed" -- from the Publisher.