Tupai is a young Polynesian girl who enjoys a peaceful existence in the hollow of an atoll with transparent water. Tireless swimmer, she dives very often with her great friend Honu, a wise and clever giant turtle. Together they never tire of exploring the seabed where Tupai discovers seashells and fish with beautiful colors while Honu delights in corals. One day one of these shells irresistibly draws Tupaï's attention : an somptuous oyster, strangely opened on the most beautiful pearl that Tupai has ever seen. Fascinated, she tries to take it... but a strange phenomenon occurs ...