Everyone in Green lawn is in a quake about the ducks that keep crossing River Road. Just when the town raises enough cash to build a special duck bridge, the money is stolen! Dink, Josh, and Ruth Rose are on a quest to find the culprit. But to catch their quarry, the kids will have to go wading... through quicksand!
In The Quicksand Question, Green Lawn is almost finished with its year-long fundraiser to build a bridge to help the local duck population safely cross River Road on their way from their nests to the water. Dink, Josh, and Ruth Rose have been saving up for the year and are just about ready to contribute their savings to the "duck bank" at the fire station; the night before they plan to turn in their money, they have a sleepover in the Pinto's barn. But Dink awakens in the middle of the night and spots an arsonist... and so the mystery begins.
As it turns out, the fire in the meadow by the Pinto's house was a decoy, and while the firefighters were busy, someone swiped the duck money. There aren't really any suspects; instead, the witness testimony has the gang looking for a mystery man with "ears like mushrooms". And their search leads them right into a perilous encounter with some riverside quicksand.
Published after I outgrew the series, The Quicksand Question was never one of the A to Z Mysteries books I read as a kid, but I'm sure I would have loved it. It's a reasonably clever mystery, at least as far as the intended audience is concerned, with an endearing touch of humor and environmentalism.