The Clue at Copper Harbor
"Becky and Sam were not thrilled about spending their summer visiting twenty-one Michigan lighthouses in three weeks, but their Mom and Dad were writing a book about lighthouses and that's exactly what they were going to do.
'It's going to be a really long summer,' Becky complained to Sam. But that was before she and Sam found out about the ghost who haunted the Copper Harbor Lighthouse on Michigan's Upper Peninsula...and before they found the mysterious notes.
Sam and Becky are soon caught up in a mystery that has them begging to return to the lighthouse. Along the way they make a friend who needs their help, and they meet some very strange characters who know more than they should about the clue at Copper Harbor."