The Invisible Island (A to Z Mysteries)

Help Dink, Josh, and Ruth Rose solve mysteries from A to Z!
 
I is for Island . . . It’s picnic time! Dink, Josh, and Ruth Rose pack up a basket and wade out to Squall Island. Right away, they find a hundred-dollar bill in the sand! But when they come back the next day, the entire island has mysteriously disappeared. What is the secret of Squall Island?