R.L. Stine 
Creep from the Deep [EPUB ebook] 

In this spinoff to the New York Times-bestselling Goosebumps series, a brother and sister searching for sunken treasure must fend off zombie pirates. Siblings Billy and Sheena always expect adventure when they join their uncle, Dr. Deep, aboard his hi-tech boat. What they don’t expect is a treasure hunt leading to a 200-year-old sea captain . . . who refuses to stay dead! Just when they think the tide is turning, Billy and Sheena accidentally drive into a dangerous mystery. Then they discover a chilling surprise awaits them in Horrorland, the theme park where their worst nightmare is about to come to life.