One fine morning, a moderate earthquake shakes the Land, causing rockslides along the bluffs. Dad quickly orders his kids under the bed. Though Dad attempts to protect Holly from harm (a few rocks fall from the cave ceiling), she reacts hysterically, believing the that quake will never end. The tremor is over within 15 seconds, but Dad leads everyone out of the cave before the aftershocks start, leaving their gear behind. Grumpy climbs out of a crack in the ground torn open from the quake.

As the Marshalls climb down, an aftershock hits, so they take cover behind the large boulder at the base of the bluff. Emily (an adult brontosaurus) goes charging through the jungle. Holly becomes nauseous, and thinks she will be sick, but Dad sternly disagrees, instructing her to breathe deeply. After she feels better, the family starts cleaning up the damage; Will and Dad piece back together their tar-sealed bamboo plumbing. Will grumbles about the culprits he theorizes must be messing with the pylons; he wonders if the pylons could control the Land's earthquakes. As Will helps Dad repair the pipeline, noting that they can reseal it with more tar from the marsh, he sees a flashing image of a face appear briefly by a bush. Soon after he describes it to Dad, the wraith-like image returns; a yellow torso with outstretched arms floats up by Holly on the rocks. Dad believes it is safe for Holly to climb down, but she foolishly decides instead to hide up in the cave. In response to Will's query, Dad describes the image as "a person who was pushed through an egg slicer".

Holly predictably screams, sending Will and Dad rushing into the cave; she is cornered by the yellow-garbed, arm-flailing ghost. The wraith enters Holly's body as she tries to flee; it speaks through her, begging the family for help. They get a good view of the wraith, which looks exactly like Holly; she herself recognizes the yellow shirt as the one lost in a bag over the falls. Will suspects the vision is a Sleestak trick, like the time they had been hypnotized to hallucinate their mother; Holly disagrees, somehow knowing the being is a benevolent alternate self. The being gestures that it wants the chance to speak, so sad asks his daughter to allow it to possess her. The entity is weak, unable to "hang on" much longer, and when asked by Dad about its location, replies that "we are half-way through". Suddenly the possessed Holly screams, and begs the Marshalls to "help Will and Daddy"; the being then exits Holly's body, whereupon she faints.

When Holly sits up, the wraith enters her once more. Apparently talking to someone unseen, she babbles "black Sleestak", "we're going home", and "don't trust him". She then goes on to describe passing through a mountain, and seeing a road with cars on it down in a valley. Dad impatiently demands to know where she is, but she instead asks them again to "help Will and Daddy". She can hang on no longer, mentioning "green stones" and warning "don't touch them" before finally floating away. Dad tells Holly that under the trance she kept asking them to "help Will and Daddy". Holly explains that it means the other Holly's family, and that the others are in trouble. She can't think of where this other family is, so Dad asks her to close her eyes and relate the first thing that comes to mind. She comes up with "rocks" and leads Will and Dad out of the cave.

Holly points in a direction 45 degrees left of straight out of the cave, but cannot explain what is all there when Dad and Will nag her to reveal more. She only knows that the other Marshalls are there, so she leads Dad and Will toward them through the jungle. Holly stops along the way, simply because she is confused; she likens her situation to being at a party, talked to by everyone at once. She gripes that the feels like a siamese twin, so Dad has her try again to close her eyes and think. Holly relates a memory of picking apples along a roadside while on a trip to Aunt Ruthie's, and notes that their mother will be worried about what is taking them so long. Will points out that by then their mother had passed away, but Holly explains that, to the other family, she was still alive. Holly wanders forward with eyes closed, depicting her alternate family's dilemma; they are stuck in solid rock, partway in stone, partway home. She points in the direction of the other family, and describes them being inside a green chamber. She warns that touching them will kill them, and the surrounding rocks must remain undisturbed as well; only the green stones can be moved. She loses her concentration, so they press on toward the other family.

Holly leads Dad and Will to a previously unknown crevasse and insists that they must reach the other side. It is narrow enough to jump across, which they do with care. A low, small cave entrance, mostly blocked with fill, lies at the base of a cliff; the other Marshalls are somewhere inside. Once Dad and Will clear away the dirt fill, Holly suddenly breaks into tears. She has lost all contact with her alternate self, and is simply too frightened to enter (geez, the script writers always seem to make an excuse why Holly can't go on the neatest adventures).

Inside the cave, whose walls are embedded with huge glowing crystals reminiscent of Enik's cavern (actually a recycled set used in "Elsewhen" sans the pylon key), Will and Dad are surprised to hear a car honking. Will becomes very excited, postulating that an open time doorway lies nearby. He boldly heads forward, but then stops when the chamber in front of him glows green. It is lined with jagged green crystals, like the inside of a geode; strange static rains and crackles within. The green room abruptly rotates 1/4 turn, squeaking like a rusty gate; Will is astonished and hesitant to enter. Dad as well considers it unsafe to enter, and believes the honking horn came from their left, so they explore the other route instead. After walking down a framed Lost City tunnel, and through a water scalloped passage, Will and Dad encounter their time-suspended alternate selves, with torsos sticking out of the wall. The other men wear clothing that Dad remembers was lost with the bag over the falls. Dad also notices a peculiar anomaly: the other Rick Marshall wears his ring on the opposite hand. A green crystal rests in the other. Dad goes on to explain his theory that the others are from a near-mirror-image universe, that is presently grinding against their own. The wall grinds and pops, further amazing Will; Dad realizes that they must act now. He points out to his son that the green crystal in his other self's hand and another two lying on the floor most likely belong in the three empty spots on the matrix table embedded high up on the wall. Will is worried about the dangers involved, but Dad feels sure that it is indeed the problem. Will easily scoops up the two crystals from the floor, but the one in the other Dad's hand poses a challenge. Dad persuades his hesitant son to climb upon his shoulders so that he can reach the one remaining green stone. He instructs Will to place the two crystals already in their possession into the matrix table. He then asks his son to get the last crystal, and warns him not to touch anything else; Dad believes, if the others are really their mirror images, they could be made of anti-matter. (He explains the consequences of annihilation to his son, or rather to the kiddie audience.) Dad coaches Will on, pressuring him with "it's now or never", and (not surprisingly) Will extracts the crystal just fine. As walls begin grinding again, Dad urgently commands Will to insert the final jewel; a bright flash, a loud boom, falling rocks, and electrical crackling all signal the momentous event. They pick themselves up off the cavern floor, finding the matrix table upright in the center of the rubble-strewn room; the other Marshalls are nowhere to be found. Will wonders if the other family "made it"; Dad replies that they will probably never find out.

That evening at dinner, which Holly is serving, Will voices his eagerness to return to the newfound cave. Dad lets him know that they will have their chance, but not until after the ground stops shaking; just then a brief aftershock hits. Will asks Dad what he thinks the other Marshalls were doing; Will himself fancies the theory that they were using the time doorway to return home when the earthquakes unfortunately hit. Dad chooses not to speculate, considering Will's idea as good as any; he simply believes that there is far more out there than they can see with their own eyes. Holly relates memories from their old house in Harrisville, where she used to see someone in her room out of the corner of her eye. Will attempts to dismiss her encounters, saying that out-of-the-corner-of-one's-eye sightings happen to everyone, but Holly fancies the belief that she was seeing her own "sister".