Simpson, Dana, 1977- Phoebe and her unicorn (Series) #21

Volume enumeration taken from spine

"In this shimmering new sequence of storylines from the world of Phoebe and her Unicorn, Marigold and Phoebe delve into the world of reading by forming their own book club. Unlikely new friendships form when Lord Splendid Humility meets Marigold's frenemy, Dakota. But there's plenty of adventure and intrigue, too, and when Marigold goes missing, Phoebe sets out to find her unicorn best friend and makes a shocking discovery."--Back cover

Includes glossary (pages 172-174; "More to explore! A special section featuring words to learn!")