Jason and Brett eagerly await the return of Neri and Charlie–as does UBRI's Dr. Hellegren who wants to study just one of the returning humpback whales, Charlie. Jason and Brett go to Neri's island to prepare for her return and find a silver pendant inside an unusual flower. When Dr. Hellegren's helicopter crashes into the ocean, Charlie calls to Neri who goes to help him but ends up being taken captive. Neri manages to escape, with a little help from Charlie, but she does so only moments before Hellegren is rescued by Captain Sam Phillips, one of the new arrivals on ORCA. Dianne's research contract is extended another six months by ORCA's new commander, her son however soon proves to be a challenge for the others. Jason and Brett welcome Neri home.

Neri makes her first visit to ORCA since her return, and tells her friends that she wants to discover who ""her people"" were. Jason, Brett and Neri go to her island to look for clues to her identity. Brett gives Neri the pendant he found in the flower, and Neri tells him it was her fathers and is a map of the island. Following clues found on the island, a large object is discovered under the island–from what they have learned so far, Jason suspects it to be a spacecraft. Mick locks Rocky in the recompression chamber.

After locating an underwater entrance to the spaceship, Neri and Jason enter the craft where they find some of her father's belongings. Taking the objects back to ORCA, one displays a holographic message from Neri's father that reveals how her people came to Earth–and that she has a sister somewhere on Earth. Kimberly challenges Mick to a race, but when she beats him, he refuses to pay up. Commander Byrne shows Dianne the top secret plans for the construction of ORCA City, she wants Dianne to do the oceanographic surveys. 1998 AWGIE Award Nominee: CHILDRENS: Screen Original (Ocean Girl Ep 16 - Jenny Sharpe

The search for Neri's sister Mera is underway. Mick asks Froggy to use his computer to change his grades but Froggy won't do it. Commander Byrne isn't pleased with her son's grades but Mick once again charms his way out of trouble. Rocky fixes up an old boat so Jason can leave ORCA as he pleases. Helping Winston with a survey, Joanne falls overboard. She is rescued by Neri, but to keep her a secret, Joanne is lead to believe that it was Winston who saved her. Dianne and Winston discover that Neri's presence enhances their scans of the seafloor. Dr. Hellegren discovers Neri is the creature that accompanies Charlie. An old newspaper article leads Jason and the others to the man who found Mera.

The kids locate Mera. Her adopted name is Jane Seaforth, and after being bounced from foster family to foster family, she is now living at an institute for gifted children. Dr. Hellegren has also found Mera and wants to take her to UBRI where he can study her. Dianne and Winston ask Neri to help with their survey while the others go ashore to find Mera. At the institute, Jason and Vanessa talk to Mera and she promises to go with them if they prove she can trust them.

Jason, Brett, Froggy, and Zoe return to the institute to get Mera but Dr. Hellegren arrives there as well wanting to take Mera back to UBRI with him. Fortunately the kids arrive in time to rescue her, convincing her she can trust them by showing her Neri's silver pendant, to which Mera has the matching piece. While the others are off rescueing Mera, Neri helps Dianne and Winston with the survey. Mick asks Vanessa to the dance as a joke but when she finds out, it is Mick who is all wet. Neri is reunited with Mera.

Mera is having a difficult time adjusting to living on the island and Neri leaves her alone while she goes to help with the survey again. Mick gets Froggy to use HELEN to spy on Vanessa's counselling session. The kids on ORCA throw a surprise birthday party for Vanessa but Mick's practical joke results in a dangerous chemical spill and fire. Jason and Brett lead a successful rescue through the air ducts. In the aftermath, it is revealed that Mick has a reading disability. Commander Byrne assigns Mick to Dianne's survey crew. Jason is not happy about his mother's developing relationship with Sam. Dr. Hellegren connects Mera's escape to ORCA.

Suspecting a connection between Neri and Jane Seaforth, Dr. Hellegren sends UBRI agents Forsyth and Liselle to ORCA to learn as much as they can about the two girls. Mick is assigned to Dianne's mission to map the ocean floor and an effort must be made to keep him from finding out about Neri who is still assisting Dianne. Mera dislikes living on Neri's island, but after Neri shows her around she begins to like the place. Sam volunteers to process the survey results for Dianne and in doing so locates a large and valuable titanium deposit. 1998 AWGIE Award Nominee: CHILDRENS: Screen Original (Ocean Girl Ep 21 - Annie Fox)

Neri returns to help Dianne with her oceanographic survey leaving Mera alone on the island to face a UBRI search party that has come to the island looking for them. Mick catches a glimpse of Neri and Mera on a monitor but everyone tries to make him think that he is just seeing things. He persists in his claim of having seen two girls but only Liselle, who is working as an UBRI spy, takes any interest. His story eventually gets back to UBRI where Dr. Hellegren plans to step up his search for the girls. When Dianne learns that Sam has been keeping his discovery of the titanium deposit a secret with hopes of cashing in on the discovery, Dianne asks him not to pursue it.

Prior to leaving on the final survey mission, Dianne learns Commander Byrne has assigned Froggy, Zoe, Joanne, Rocky and Kimberly to her crew. Forsyth hides a transmitter on the boat to allow UBRI to follow it. UBRI divers are dispatched to apprehend Neri and Mera and in their struggle with the UBRI divers, Neri and Mera are caught by the boat's cameras for all to see, revealing their existence to everybody on board. Responding to Mera's call for help, Charlie intervenes allowing the girls to escape, it's the first time Mera has been able to talk to Charlie. After being told about Neri and her sister, the kids all agree to keep the secret, except for Mick who just says that he'll ""think about it.""

Jason takes Neri and Mera swimming off the ORCA platform. Mick finds out and heads out on a jetski, he falls off and must be rescued by the girls. Neri helps Mick with his reading, he in turn joins the others in keeping Neri and Mera a secret. Forsythe tries to get access to Dianne's research and cripples HELEN in the process, in the confusion Lyselle sees Mera in the coridor and reports back to Dr. Hellegren that Neri and Mera are on ORCA. Winston, receiving strange signals from Neri's island, goes to investigate and meets two strangers, but back on ORCA he says his trip was uneventfull.

Neri leaves ORCA intending to save Mera and Charlie by giving herself up to UBRI. Brett chases after her, gets into an accident with a UBRI boat and is saved by Neri. Sam destroys his remaining records of the titanium deposit. Winston continues to secretly meet with the two strangers. Unable to bring the girls back to the island, Winston takes the two strangers to ORCA where they tell Neri and Mera that they have come to take them back to the Ocean Planet, their home. Vanessa helps Mick with his reading and defends him when Commander Byrne accuses him of slacking off.

Neri and Mera make the decision to return to the Ocean Planet and convince Diane that her research must continue. Froggy fixes HELEN, with a little help from Damien. Commander Byrne has Forsythe arrested when HELEN identifies him as the sabateur. The kids take care of Liselle, keeping her from contacting UBRI. Neri and Mera are taken back to the island, with Winston, Mick and Zoe acting as decoys to keep UBRI away. Final goodbyes are said as the girls board the spacecraft for home but after the ship leaves, one person has stayed behind. Neri says she must stay to ""finish father's work.""

Mera's spacecraft splashes down in the ocean and as she swims to the surface she is surrounded by Commandoes. Seeing the craft come down from the island, Brett, Neri and Jason rush out to rescue Mera. Once safely back on Neri's island, Mera tells of the spread of the red virus on the Ocean planet, the rebel's growing power, and their plans to invade the Earth after melting the polar ice caps. Malakat and Shersheba make arrangements to return to Earth while Neri hides the new ankh in the river near the Bates' farm. Winston picks up Praxis radar activity near ORCA. Agent Shelby has monitored Mera's craft as it arrived on Earth and after connecting it with previous activity in the area, he is able to get Project Pheonix reopened. Neri observes Shersheba returning to the pyramid with her commandoes.

Jason and Winston climb the mountain on Neri's island to install surveillance equipment. Making their descent, Winston is bitten by a snake and falls the rest of the way down. Meanwhile back on ORCA, technicians are preparing to upgrade Helen but when they shut her down improperly, the entire station loses power. Neri and Brett trek across the island for a rare flower that can counteract the snake venom while Cass leads the effort to get Helen back online. On the distant Planet of the Oceans, a fast acting virus has ravaged the world's oceans and Malakat, as the leader of the rebel faction, plans an invasion of the Earth. On ORCA, a signal from deep space has been picked up by the receiver on Neri's island—it is Malakat scanning for any signs of the underwater pyramid.

Richter talks Elly Hauser into rejoining agent Shelby on newly a reopened Project Phoenix. Winston, Cass and Brett program Helen to provide 'just the facts' if questioned about pyramids. Louis overhears them trio talking about pyramids and tells Shelby and Hauser what they're doing. After a little prodding by Shelby, Helen reveals the existence of the underwater pyramid to the Praxis agents. Shersheba leads a group of commandos in a search of the nearby islands for Neri and Mera but they are unsuccessful until Brett is observed in a boat heading towards an island, Shersheba informs Malakat of this and plans a search of this island. After showing her around the station, Louis challenges Ilona in a race to the galley.

Vanessa Lane comes to ORCA and ends up in the same class as Jason. Brett, Zoe and Froggy play a trick on Vanessa and she gets back at Brett and leaves him in a broken boat out at sea. A storm comes up, so they can't search for him. He strands on Neri's island and meets Neri, and tells Jason about her when he comes back.

Neri is taken back to Praxis headquarters where she is interrogated. Neri's captures prompts Jason to put the Ankh out of reach of Malakat and Shersheba, he drops it into the deep ocean. Neri's deteriorating condition and Praxis's uncaring treatment of her results in Hauser developing a sympathetic attitude towards Neri. By showing Jason footage of Neri from Praxis's own security cameras, Shersheba convinces Jason that tshe and Malakat have Neri and offers to return her in exchange for the Ankh. Jason and Brett arrive at the transfer location but Shersheba, disguised as Neri, grabs the Ankh and runs back to Malakat, at which time they discover the Ankh to be a copy. Later, Shersheba sneaks back onto ORCA and, with help from Louis, is able to discover the location of the real Ankh. She retrieves it and returns triumphantly to Malakat.

Budds Praxis begins moving their equipment onto ORCA, including several nuclear weapons. Jason and Brett travel to the underwater pyramid to propose a meeting with Malakat of Neri's behalf. Hauser is opposed to Shelby's heavy-handed approach to dealing with the aliens. Neri meets with Malakat on a deserted beach, during their talk, Malakat reveal that he was responsible for her mother's death. Meanwhile, Mera is captured by Shersheba and her commandos, she will only be released in exchange for the ankh. Richter arrives on ORCA and assumes command of the station. Neri is torn over the decision on whether or not to exchange the ankh for her sister, Jason won't help her telling her it is a decision only she can make.

Dianne is at ORCA Pacific headquarters for her interview, she is surprised to discover her exhusband in the role of interviewer and more surprised to learn the job is hers if she wants it. A return visit is made to the pyramid by Neri, Jason, and Brett. Neri finds a way in and the boys follow in the minifin.Exploring the pyramids interior, Neri activates a holographic recording which relays a cryptic message about a quest. A doorway is opened revealing a swirling vortex which pulls the trio in. They reemerge in another pyramid, and upon exiting, discover that they are in Egypt! Agents Shelby and Hauser begin their search for the receivers of the alien transmissions while Malakat and Shersheba continue their own search.1998 AFI award nominee: ""Best Childrens Television Drama"" (Jonathan M. Shiff)

On the Ocean Planet, Mera is pursued by the rebels but is able to reach safety in the Pyramid of the Elders. A group of rebels arrives on Earth. They pursue Neri are driven off by Jason and Brett in the minifin. Shersheba leads an assault on the Pyramid of the Elders. Mera escapes to Earth with a new Golden Ankh moments before the elders trigger the destruction of the pyramid. As the Pyramid of the Elders is destroyed on the Ocean Planet, back on Earth, the underwater pyramid returns.

Dianne Bates and her sons Jason and Bret come to the underwater base ORCA for six months. They meet Winston Seth which is Dianne's assistant. Sher is going to study whales. Brett finds the place cool, but Jason donesn't like it. They also meet commander Lucas. At dinner Brett meets his new friends Zoe and Froggy whos real name is Jake Reilly{}. Dianne, Winstorn, Jason and Brett go out with the boat to put a transmitter on the whale. A girl comes up out of the ocean and stops Jason when he is about to shoot the transmitter on the whale, so Dianne has to do it instead. Nobody believes Jason when he tells them about the mermaid.

Praxis's return to ORCA prompts Cass and Brett to seek Winston's help to delete all of Helen's records of Neri. Louis observes them through the airduct and informs Shelby and Hauser of what is happening but by the time the agents react, all of the records have been erased. Neri and Jason dive to the underwater pyramid, Neri activates the Shalamorn hologram and the pair are told about a rebel faction on the Ocean Planet that is opposed to a peaceful migration to earth. Soon after Malakat and Shersheba arrive and tell Neri and Jason of their own plans, as part of the rebel group, to use the power of the pyramid to melt Earth's polar icecap to prepare the planet for their people's arrival. Malakat also tells Neri that he caused the spacecraft that she and her father were on to crash to earth. Malakat demands the Golden Ankh be tuned over to him, but Neri and Jason escape through the water gate. They emerge in the same cave in the outback that they were in before and find Jakamarra waiting

Shelby requisitions the minifin to get a closer look at the underwater pyramid, Diane assigns a reluctant Jason as his pilot. Near the pyramid, they encounter a group of commandos and come under attack. The minifin loses power and heads to the ocean floor. Jason is able to jump start the minifin using the battery from Shelby's GPS receiver and brings them safely back to ORCA. Shersheba and her commandos search Neri's island, Neri and Mera hide in a cave but when Shersheba closes in, she and her commandos are frightened off by a group of birds. Ilona eavesdrops on Shelby's report to Richter and reports what she's heard back to Malakat. Hauser interrupts Ilona's transmission and begins to grows suspicious of Ilona. The president of the Global union gives Praxis the authority to take over ORCA to use as a base from which to attack the underwater pyramid.

Neri, Jason, and Brett wander into an archeological dig and meet Professor Malakat and Shersheba. Finding the minifin abandoned, Winston tracks the signal from Brett's vid-phone to Egypt, but discounts his findings as a phantom signal. Back in Egypt, Malakat begins to take an interest in the travelers he's taken in, he has Shersheba befriend Jason hoping to find out more about Neri. Jason is able to make a quick phone call to ORCA and tells Cass where they are. Not long after, Malakat is in contact with the boys mother promising to send them back to Australia, he then tells Jason that Neri will have to stay behind due to problems verifying her identity. From an analysis of the material in Neri's clothes, Malakat determines that she is not from Earth and when Shelby and Hauser enter the camp, he directs the agents to the kids. Forced to make a quick escape, Jason commandeers a jeep and the trio drive off, joining a tour group headed back to the ""Pyramid of Mystery."