Simon and Molly are best friends. They love to play hide and seek, even though Simon says that Molly is too easy to find. But one day, Molly hides so well that Simon can't find her anywhere. Where is Molly? Is she truly missing? Simon looks for Molly everywhere — under the sink, behind the chair, in the toy box. Molly is missing! Things grow even more mysterious when a stranger appears at the door to help Simon look for the missing Molly. Lisa Jahn-Clough's simple text and colorful artwork will have children engrossed in the search for Simon's best friend. And they may even figure out who the mysterious stranger is before Simon does.