Mark befriends a boy whose family is vacationing on a houseboat in the river. While out on an adventure together a hurricane quickly comes in. They get the boy's mother from the houseboat and Ben leads them to the safety of a cave.

As Tom and Mark are watching a mother bear play with its cub the mother gets shot by a swamp hunter. Tom issues as citation to the hunter and takes the cub. Ben appears to be jealous of the cub and when the hunter's boy steals the cub Mark assumes Ben chased it off. They discover that the boy stole the cub because living in the swamp he had no friends or pets. In an on the spot judgement, Tom tells the boy that the terms of his probation are to take good care of the cub, and the boy's father goes along with it.

Ben and Mark stumble upon fish poachers and their illegal smokehouse. The men threaten to kill Ben if Mark tells his father. Later Ben wanders off and Mark follows him onto the poachers' boat; they hide but the boat takes off when they hear Tom's airboat approaching. When they start shooting at Tom, Mark and Ben come to his rescue and the poachers are arrested.

Mark befriends shoeless Jenny Maddox at school. However, when Tom drops her off at her father's dock in the airboat, he discovers that Jenny's father is the alligator poacher he has been looking for. Before he goes back to arrest him, Jenny's father saves Mark from an alligator. Tom thanks him for saving Mark but still has to run him in, although he offers to help him in any way he can.

Mark gets Tom to put a radio transmitter on Ben so he can hear what he's doing when he's away. After Ben wanders off a plane carrying exotic animals crashes in the bush. Ben runs across the plane and when Mark hears the moans of the co-pilot, he figures out where he is and goes to help him. Finding the plane and the injured pilot and co-pilot, Mark calls in the location with Ben's radio. One of the animals is a tiger, whose cage has broken open- Ben protects Mark and the co-pilot. Tom and Ellen then arrive in the jeep and tranquilize the tiger.