Robby Hoenig, his parents, and his best friend Harry Smith are in Hawaii for summer vacation as well as visiting Robby's grandfather and his dolphin research center. But while there, two mysteries surface, a dolphin was found injured and one of the scientists has gone missing. as the family dives deeper to get to the bottom of it, more mysteries surface and they find out more than they bargained for. For those who have read the Treasure at Dolphin bay, which is a Hardy boys book, this kinda starts off the same, and then becomes its own thing. Characters are from that book and Secrets of the Deep trilogy by Gordon R. Dickson. Hope you like it!!