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.

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.

While on a shopping trip, Ben climbs into a delivery truck and gets separated from the Mark and Ellen. Subsequently Ben has a number of solo adventures including licking the shaving cream off of a man's face in a barber shop, ending up at a garbage dump after looking for food in a dumpster, and jumping off a railway bridge as a train heads towards him. Part one of two.

An injured Ben wanders into the camp of a couple of old carneys whose own bear is too old to perform anymore. They are going to keep Ben and train him but an announcement on the radio encourages them to return him to Mark.

Right after Mark has been teased by girls on the school boat, his cousin Virginia comes to stay with the Wedloes for the weekend. Mark tries to entertain her but she is reluctant to do anything. Mark and Virginia find an old sea mine in the channel while fishing and she won't help him move it so he goes to his father for help. Virginia talks to Ellen about being afraid, and Virginia decides to face her fears by taking Ben and some rope to move the mine. When Tom hears of this, he, Mark and Boomhauer race to stop her. They get her and Ben to safety just as the mine explodes.

A dolphin comes up the channel and hangs around the Wedloe's dock. He and Ben become friends and Mark considers him his pet. Mark is disappointed when he finds out that the dolphin escaped from Miami Seaquarium and has to go back before he is lured by the wild dolphins at sea in mating season. The lure of mating season is too strong for the dolphin, Marco Polo, and he heads to sea with Ben following.

Mark is despondent as he has not just lost his new pet, Marco Polo, but his old pet Ben. Frank from Seaquarium takes Mark and Tom out on a boat to find Ben and Marco Polo. They spot Ben on a small island and as they get his attention and he swims for the boat he is threatened by a shark. Marco Polo comes to the rescue and nudges the shark away from Ben. Ben climbs a ladder to get onto the boat, and Marco Polo is returned to Seaquarium.