Andre Norton 
Key Out of Time [EPUB ebook] 

Sent from Terra to probe the past of the deserted planet Hawaika, Time Agents Ross Murdock and Gordon Ashe are startled when murky underwater pictures of ancient races locked in a fierce battle for supremacy suddenly appear on their time-probe. Despite prophetic warnings of Karara, a Polynesian girl, the Agents decide to invade the past and uncover the secrets of this barren, lotus world.