Once, there were two best friends. One was from the sea, a mermaid named Merrin, and one was from the land, a human named Molly. Of course Merrin has never been to Molly's house; how can she visit when she must stay underwater? But then comes the night of the Mermaid Moon, when sea creatures can fly through the air! And this year, Merrin is finally old enough to join in. Together she and Molly visit the Mermaid Moon festival, eat ice cream, and ride on a swing in Molly's backyard. But when it is time for Merrin to leave--the moon is sinking toward the sea--she is unable to get down from a tree the girls have climbed. And if she doesn't get back home before the moon sets, the Mermaid Moon magic will disappear from the earth forever.   Here is a delightful and dramatic picture book that makes every girl's dream of being friends with a mermaid come true!