Elizabeth and her father have been getting to the bottom of some minimal, but instructive and simply worded, mysteries for some time to the delight of newly independent readers. (Elizabeth the Bird Watcher, 1963, and Elizabeth the Treasure Hunter, 1964.) This scrap of adventure has more humor due to the determined interference of one of Elizabeth's playmates. Stewart, a talky and brainy boy, keeps arriving to upset the detecting plans of Elizabeth and her father who are set on solving the identity and the predicament of a strange bird whose hair-raising cry from the marsh sounds like Stewart's worst moments on his bugle. Just as good conservationist birdlovers should, they rescue a downed and off course sand-hill crane.