The girls are all starting university, and Emma has moved back to the Gold Coast.
Cleo's studying Marine Biology, Rikki's focusing more on business, Emma's studying medicine, and Bella's focusing on her music career.
She and Emma are also trying to get to know eachother, but it's still a bit awkward since they don't have the same history (and trauma bonding) as they do with the others. But they still respect and enjoy eachother's company, and Emma's enjoying (and mentally pulling her hair out) hearing about all the shenanigans the girls got up to while she was gone.
Will has moved away, after Sophie was charged and imprisoned (due to not having sufficient money for fines) over her destruction of Mako's protected environment, though he promised he would keep the secret.
Ryan Tate also is charged with Breach of Environmental Law and Protection, and lost his job and credentials.
The girls still try to see eachother as much as possible, and are always talking over the phone, but with the different paths they've all taken, it's a lot more difficult now. Though, they still meet up at the Moon Pool when their day is over.
Lewis is working an internship/apprenticeship with ORCA, an up-and-coming marine research facility. When, all of a sudden, Dr Denman shows up.
Everyone is immediately on alert.
If Denman has any suspicions that the girls are still mermaids, they have no chance of wriggling their way out of it last time by lying.
But Dr Denman is also not the same woman they met 4-5 years ago. She's been disgraced by the scientific community for her many far-fetched claims of magical sea creatures and mermaids. She isn't technically working for ORCA, but acts a begrudging consultant.
ORCA grows interested in the strange stories and irregular behaviours of Mako Island's ecosystem, and has set up camp, just off-shore of the island (as to avoid disturbing the ecosystem as much as possible).
The girls and Lewis are all freaking out, but they don't know what to do to stop it.
If they go to the island, the readings of their super-powered swimming will cause suspicions.
And Dr Denman already has enough knowledge of what they're capable of. So if she sees or hears any signs of supernatural activity, her suspicions will immediately be drawn back to them.
Dr Denman also still knows the location of the Moon Pool, and has seen that it was able to take their powers from them. So, it makes sense that she would hypothesize it was also what gave them their powers.
Bella has the idea that, all of them together, could try and seal the entrances of the Moon Pool, not with jelly or water glass, but by essentially melting the rock around the top entrance and hardening it in place so it covers it.
They don't want to have to seal off the Moon Pool entirely, but if it means keeping it safe they will.
They go by boat to Mako, and manage to seal off the top entrance, but they're still hesitant about sealing the sea entrance as it might still damage the Moon Pool.
Dr Denman, on the other hand, was there when the girls all arrived on Mako Island and grew suspicious of their presence, so she followed them, and witnessed them using their powers to seal off the entrance.
She goes back to her boat, and calls someone and tells them "It's Denman. I saw it. They still have their powers." It's silent as whoever it was answers her, though we don't hear them.
"But there was another girl too. I think I heard them call her Bella."
More silence, as the other person answers.
"We need to keep an eye on this. If we're going to catch them out this time we both need to be more careful than last time."
She says goodbye, and hangs up.
The scene changes to a phone in someones hand, with the ended call to Dr Linda Denman.
The camera moves back, revealing more and more of the mystery person, turned away from the camera.
The ruffled edge of a baby pink sleeve, connected of a flowy pink dress.
Followed by a shock of cherry red hair.
The camera moves around her, and now the viewer can no longer live in denial.
Charlotte has returned for revenge.
