Invisible Island Series

Includes Invisible Island, Dig for a Treasure and Wish on the Moon.
Books in the Invisible Island series:
Invisible Island (1948)

The four Guthrie children are cast away on an invisible island.
Dig for a Treasure (1949)

A treasure is rumored to be buried on Invisible Island, and the eight explorers are determined to find it.
Wish on the Moon (1951)

A Halloween mystery for the Guthries and their friends.