The Mystery of the Purple Pool

Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather and they're going on an exciting trip to New York City! The children have a great time visiting the Empire State Building and ice skating at Rockefeller Center. But they discover something very strange at the hotel swimming pool: Someone has dyed the water bright purple! Who would do that? And why?