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.""

Winston calls Diane and her sons back from their vacation informing them that UBRI has won the contract to construct ORCA City and their plans threaten a nearby fish breading ground. Dianne, as ORCA's new environmental officer, quickly calls a stop to the construction and begins a environmental study of the site. A dive to collect samples sees Jason become trapped under a fallen strut. As a rescue party is assembled, Charlie calls Neri who comes to save Jason as his air is about to run out. Dianne takes her case against UBRI before a tribunal who rule in her favour, stopping UBRI's construction. Dr. Hellegren's plans to destroy the breeding ground are thwarted by Neri. Hellegren warns Jason and Brett not to interfere with him.

Brett talks Jason and Neri into looking for a way into the spacecreaft they found buried on Neri's island  their search is unsuccessful. Brett and Benny meet Cassandra, a new arrival from ORCA's sister station near Florida. Cass takes out a sailboat, but with a storm coming and a damaged sail, she seeks shelter on Neri's island. The following day Neri finds an entrance to the spaceship that was uncovered by the storm. When Jason and Brett come to the island, Cass sees them with Neri before fixing the sail on her boat and heading back to ORCA. Distracted by the sight of Neri in the water ahead of her, Cass is struck by the boat's boom and is knocked unconscious. Back on ORCA an anxious Jason and Brett discover Cass has amnesia and cannot rememeber what happened to her. Jason tells Brett to become friends with Cass to keep her from telling about Neri if she gets her memory back. Dr. Hellegren goes to visit his daughter at her boarding school, she pleads with him to be allowed to spend h

Jason and Brett steal a pump from UBRI supplies on ORCA so they can pump out the spaceship. Cass and Brett trade practical jokes but when they team up to get Cass's sister Morgan, they also catch the Commander in their soapy trap. Jason is teamed up with Sallyanne for a training exercise, but their first drill does not go well. With the spacecraft pumped out, Neri and Jason enter the ship. They are joined by Brett, who has been scrubbing the floors on ORCA for his role in the practical joke on Morgan, and the trio come across a person in a sealed chamber, still alive

Jason and Brett are about to force the chamber open when Neri finds the controls that open the chamber and revive it's occupant. He comes to and says his name is Kal. He is shown around the island where he seems to be content to live. Brett and Jason are surprised when Kal says he will take a subordinate role in relation to Neri, as is done on his own planet. Benny covers for a girl caught cheeting on an exam and is also disqualified. Lena Hellegren makes a surprise appearance at UBRI forcing her father to take her home where she convinces him to let her remain instead of being shipped off on vacation by herself.

Concerned about Kal's development, Neri asks Jason to talk to him. After telling him to stay on the island, Kal follows Neri to ORCA. Brett, Benny and Cass are given diving classes for their failed practical joke on Morgan. After their lesson, Benny sees Kal aboard the boat starting the motor and then diving overboard, he tries to tell people what he saw be no one will believe him and instead accuse him of starting the boat. Dr. Hellegren brings Lena to ORCA where Jason and Brett tell her about some of the things her father has done but she won't believe them.

Hoping to keep Kal from making any return trips to ORCA, Jason suggests to Neri that she show him around the spaceship which he has been interested in. Winston's inability to swim is made an issue of by Kellar and UBRI, threatening his job on ORCA as they hope to replace him with one of their own. Fortunately, Benny discovers a provision is the regulations forcing the commander to give Winston a week to meet the qualifications. Neri brings Jason and Brett back to the ship where she and Kal have made a discovery. An interface with the ship's computer gives Neri access the ship's log written by Kal's mother. She explains to the group about a mission requiring the assembly of nine pieces of ""Synchronium"" which once put together will have the power to heal the Earth's oceans. Neri asks Jason and Brett to help her look for the Synchronium but they must no tell anyone else. Believing that Neri is close by to assist him, Winston passes his swimming test.

Neri goes to ORCA to see how Jason and Brett are going with their search for the Synchronium. Dianne takes the opportunity to ask her to help Winston with his dive test which she agrees to do. When Neri doesn't return to the island on time, Kal takes the opportunity to go back to ORCA. On ORCA, Kal manages to get signed up for Morgan's fitness class (she's very impressed with him) and gets a date with Marika, which Jason is able to speed him through. Neri helps Winston through his test by getting him to believe in himself. After Lena's visit to ORCA, Kellar warns her that her curiosity may reveal things about her father she might not want to know.

Neri awakes on the island to find Kal missing, he's gone to ORCA. Jason and Brett introduce Kal to Diane and Winston. Shortly after, Neri arrives and tells Diane about UBRI's plans to use explosives on the ocean floor in their construction. Diane is not happy and takes the issue before the tribunal but unfortunately they rule in favour of UBRI and allow the blasting to proceed. Jason and Brett begin searching HELEN for reports of UFOs and meteorite impacts that may help them locate the Synchronium pieces. Neri senses something wrong with the oceans but cannot be more specific. Successful in their search, Jason, Brett, and Neri venture inland to retrieve the first piece of Synchronium. Lena accesses her father's locked computer files. Kal beats Benny, the youth champion, in a game of trigammono.

Brett locates another piece of Synchronium but interrupts Jason's training exercise to tell him the news. UBRI has also located the piece and mount an effort to retrieve it. Lena is back on ORCA looking for clarification about her father, she learns nothing from Brett but does meet Kal. Jason, Brett, and Neri go after the second piece of Synchronium, it is far inland and they must go by camel. Arriving after UBRI, who have already recovered the Synchronium, the trio is spotted and pursued by Kellar who they are able to elude on their sure-footed camels. Dr. Hellegren begins studying the piece of Synchronium and discovers that it generates a tidal force.

Neri moves the Synchronium piece to her secret underwater cave to keep it safe. Benny's father chastises him for spending time with Brett and Cass instead of studying. Cass finds a young boy on ORCA who swam to ORCA from the ship that was taking him and his family home after they were refused refugee status, she keeps him a secret and brings him food. Brett and Benny go in search of sunken treasure but when a valuable piece of equipment falls overboard, Benny goes after it and runs out of oxygen. Charlie calls Neri to rescue him revealing to him her presence. Benny lies to the commander about the incident to keep Neri a secret. Cass' stowaway is discovered and he is turned over to immigration officials. Lena gains access to her father's files about Neri.

A trip to ORCA prompts a discussion between Neri and Kal about feelings. Cass is beginning to remember about her time on Neri's island in her dreams. Brett takes Benny to the island to see Neri and Kal and Jason arrives soon after having discovered the location of another piece of Synchronium deep in the ocean. Neri is anxious to retrieve it and sets out by herself. The boat taking Brett and Benny back to ORCA breaks down, and with strict instructions not to go to ORCA, Kal abandons them in the middle of nowhere. Fortunately, Charlie alerts Neri, who was unsuccessful in her attempt at retrieving the Synchronium, and she comes to their rescue. Back on ORCA Brett is hassled by Moose, a bully who demands his new satellite navigation unit. With Jason and Brett assisting her, Neri retrieves the Synchronium from the ocean depths just moments before UBRI arrives on the scene. Brett is again confronted by Moose but Kal, acting on the lesson he received on loyalty after abandoning Brett and Ben

Neri continues to teach Kal about feelings. Cass is still having her dreams about her time on Neri's island and now remembers Brett being there. Lena overhears her father and Kellar talking about their plans for creating a news bulletin to lure some of the kids from ORCA to an island to find out exactly what they know about the alien device. Jason is uneasy about his helicopter flight test and is unable take the controls. Kal searches the spaceship for a gift left to him by his parents. Benny and Brett arrive and find him playing a strange musical instrument and crying, Brett explains to Kal why people cry. Seeing the news bulletin created by UBRI, Brett and Neri head off to the remote island looking what they believe to be another piece of the Synchronium. Lena arrives on ORCA to warn the Bates brothers about the trap but she is too late to stop Brett, she does find Jason and warn him. Needing to get to Brett and Neri quickly, Jason goes on another helicopter test with Morgan and dive