Rex, Danny, and Susie enter a cave containing Lost River, whose outlet has never been found. A giant bat attacks, but Rex kills it. A cave-in forces them to swim underwater only to meet a bear that Rex bowls into the water. They exit to find an undiscovered waterfall now named Rex Falls!; Rex and Danny visit a cranky uncle, but he leaves them home to go prospecting. The aunt takes them to the circus, but a killer tiger escapes - and heads to the Painted Mountains where the uncle is alone! Rex races, dodges a bison, and meets the tiger about to make a kill. Rex drags branches for a tiger trap and catches the big cat, fetches water for the old man, and waggles a signal torch for a helicopter. Rex and Danny are welcome back any time to go prospecting!; Sheriff Chase and Bobo the Detective Chimp take a much-needed vacation, a three-day fishing cruise. But a rich jerk is murdered and his money stolen. As the Sheriff interviews suspects, Bobo keeps fishing. He's attacked by a masked killer, but Bobo flicks his fishing rod, snatches the gun, and wallops his assailant! Bobo then pulls up a dead fish holding the money stolen by the first mate. Bobo even gets his photo in the paper for bagging the biggest fish!