The Alden children are going on a trip to Grandfather's friend who lives in a cabin along the Mississippi River. The kids are so excited---they even get to take a trip down the Mississippi River on a paddle-wheel boat! But once the kids arrive, they realize that strange things have been happening. . . Cap's been receiving odd phone calls with someone breathing on the line, and holes are popping up all over the property. It sounds like another mystery, and the Boxcar Children are on the case! #20 in the series.