The Aldens are off on another adventure in The Mystery in the Cave. The kids are so excited to test out their cave and spelunking knowledge when they go to visit the Dragon's Mouth Cavern. When Benny discovers a sinkhole that leads to an undiscovered underground cave, the kids find themselves immersed in a mystery that may involve a monster. . . and someone definitely doesn't want them looking around in the caves! Can the Boxcar Children solve this mystery? #50 in the series.