While trying to get to the carrot patch, Will and Holly run into one dinosaur after another: first they bump into Big Alice dining on her latest kill, then they are charged at by Spike. Will suggests going to a place he knows where there won't be any dinosaurs -- up on the mountaintop to investigate a golden glean shining from there -- but Holly is against the idea, pointing out that Will's last discovery of a faraway shimmer resulted in Dad's getting shocked by two blue crystals (Holly must not remember well; it was a triple combination of yellow, red and blue). Holly also argues that she is afraid of heights, but after Will assures her that she'll be alright, that it would be fun, that they have already learned to be careful with crystals, and that they won't run into Grumpy or any dinosaurs up there, Holly agrees. She dashes off to begin their adventure, with Will close behind.

On their way up the mountain, the kids take a break from climbing and rest on a ledge. Holly enjoys the view and realizes that her concentration on climbing has kept her from getting scared. Within a moment, they continue their trek to the top.

At the summit, Will and Holly discover a glimmering pylon. Holly warns her brother to be careful if he opens it up, so Will promises (falsely) that he's only going to look. Holly scolds him when his tinkering invokes lightning, but her efforts are fruitless; Will insincerely apologizes, then insists he knows what he's doing while he continues to recklessly experiment with the matrix control table. After causing some more lightning, Will somehow conjures up a green glow moving across the sky. The green glow emits a fast-moving red glow; a parachutist in turn ejects from it. Will realizes that he's opened a time doorway, and if they could only reach it, the whole family could return home! Holly reminds her brother that they'd better go see who came down on the parachute that landed near the swamp, so the kids hurry on down to make sure that he's alright.

Will and Holly arrive to find their newcomer stuck in a tree, enduring harassment by Spot. After Will shoos the coelophysis away, he introduces himself and his sister; the parachutist identifies himself as Beauregard Jackson of Fort Worth, Texas. Will invites Mr. Jackson to their cave and helps him down from his parachute tangled in the tree.

Back at High Bluff, Will introduces their guest to Dad, who is busy making their supper. Mr. Jackson requests directions to the nearest telephone (referring to Mission Control), but Dad comes across as telling tall Texas tales when he tries to explain to the man that they are in another universe, inhabited by huge dinosaurs, monkey-like Pakuni, and giant-insect-like Sleestak. Their guest is rudely awakened to the reality of his situation when Grumpy pays them a visit for another dose of the Flyswatter.

That evening around the campfire, Mr. Jackson recalls the re-entry of his hypersonic glider (not an interplanetary vessel) over Ecuador, returning from a routine transit between Phoenix Port and Space Station 5. At the time, he couldn't see too much due the plasma field building up over the heat shields. His glider's tail was suddenly severed, and the next thing he knew, he was stuck in his parachute hanging from a tree. Jackson remembers the radio in his capsule, but realizes it won't do any good where he is now. Dad assures him that there's a way out through the time doorways, according to their non-human friend Enik, and that the many pylons around may have the potential to open unto other places and times. As the adults hit the sack, the kids clean up. Holly reminds her brother that he will eventually have to confess his responsibility for Jackson's predicament; after Will promises he'll explain to the adults tomorrow, he notices the unusually noisy wind outside.

Trekking through the jungle the next day, Jackson asks Mr. Marshall about the green glow moving across the sky. Will quickly admits to everything; luckily, the adults are understanding. The space pilot excitedly proposes that they could pass back through the doorway to return to Earth about 20 years after the Marshalls had left; Dad, approximating the altitude of the moving time portal at 50 or 60 meters, suggests they could climb to that elevation and jump through. Will even speculates that they could use the pylon to guide the doorway into position; with Mr. Jackson's support, Dad concedes. With everyone excited about the possibility of returning home, they all head over to the swamp to recover the glider pilot's survival kit, binoculars, and parachute.

When the kids question Mr. Jackson about the need for his parachute, the pilot explains that he was 15 miles up, moving at 1/2 mile per second when he passed through the time doorway; Earth's side of the time portal presumably is still at that height and speed, which is the logical source of the wind. He further explains that after passing through the doorway, he'll freefall to the lower atmosphere and parachute from there. After Dad points out that his family members have no parachutes of their own, Mr. Jackson promises to return with a ship to pick them up.

At the mountaintop, Jackson insists that they'll have to use the pylon to guide the doorway closer to a hilltop, since it appears to approach only one which is very far away. Once he takes a closer look with his binoculars, everyone in turn witnesses firsthand the startling truth of their small, unbounded, finite universe: the faraway hill is the very hill they're on; looking ahead through the binoculars, they view themselves from behind. As the kids marvel at a second glimpse, Dad takes Mr. Jackson aside to remark on the unfeasibility of a rescue attempt; the rapidly moving time doorway would not only be impossible to intentionally re-enter from Earth, bust must be quickly closed before the increasing influx of air into the valley creates a hurricane.

Holly spots some Skylons, which signal a pattern of green-yellow-red, blue-yellow-red. Marshall and Jackson enter the pylon to "key in" the skylons' requested sequence; Jackson is perplexed by the large pocket of space inside the small pylon. Dad enters green-yellow-red, blue-yellow-red, red-yellow-red; the wind is slightly affected. Will reports a new sequence, green-yellow-green, blue-yellow-green, red-yellow-green, which only fuel's the gales ferocity. The adverse result is explained when Dad realizes that the Skylons can only properly regulate weather native to the valley, and cannot cope with extra-dimensional influences. After Holly also reports a Skylon's consumption by the time doorway, Mr. Jackson demands they that redouble their efforts on getting through the portal. Dad understands his anxiety, but to protect everyone's life, he insists it that it very soon either be slowed down or shut down. Jackson concedes that priority, but adds that they should take advantage of gaining any directional control of it in the process.

Dad's first experiment with the matrix table results in only lightning, but he is soon able to alter the doorway's speed and direction. Its new path intercepts the mountain further below; the time portal burrows right through, causing an earth-shaking explosion. With Jackson's guidance, Dad is able to turn, decelerate, and raise the doorway up to their altitude, where it is now heading straight at them. In the raging wind, Mr. Jackson fastens down his parachute straps and bids the family goodbye as the Marshalls duck for cover behind a very cheap set of boulders in front of a featureless blue background. The green time doorway passes directly across the hilltop's surface, consuming the pylon as well as the spaceglider pilot; with the portal's power source gone, it too disappears. As Dad comments on the destruction of the pylon and gateway, Will suggests they find another to experiment with. Dad's initial reaction is anger and scolding, but reflecting upon the opportunity his son's tinkering gave them, he eases back and smiles.