Book 18 of the series emphasizes the diphthongs "ue" and ew" which make the same sound. The story follows Sue, a mom with a blue Jewel that goes missing. This book continues the fifth set of the series (books 16-19), which emphasizes the diphthong combinations of two sets of two-letter combinations that make the same sounds. Look for all of the books within this set of the series, which emphasize the oy & oi set, the ou & ow set, the ue & ew set, and the au & aw set.