Dive into the undersea world of mermaids and join in their amazing adventures. Harmony braves the spooky Pirates' Graveyard. Marina takes on her rivals in the Great Seahorse Race. And dance-crazy Coral makes a bargain with King Neptune.

USBORNE图书馆系列到LEVEL5之后，词汇量增加到1000-1500，每页的文字数量在十行左右，共48页，涵盖了英文大部分的语态和时态。从这个级别开始，由图画书逐渐过渡到章节阅读。适合小学五六年级和初中生作为词汇量扩展读本。Level5系列均为世界知名的民间故事和童话故事，学生一般都已接触过中文版本。