Ant and Fontaine realise that their grandparents found Lemuria before them - but where are they now? The Nektons follow the trail they left but run into giant, predatory Sand Strikers. Was this the fate of their grandparents?

Ant searches a deep chasm for clues to his grandparents' fate but is stunned to find Mad Madeline there. She has been looking for the biggest sunken treasure ever, but all she has managed to find is the biggest monster.

Three baby Monumential turtles hatch, and they are the size of city blocks. The playful babies accidentally sink a fishing trawler. Can the Nektons wrangle these creatures before they sink even more ships?

Does Dolos really have a lead on finding Ant’s grandparents? Or is he leading the Nektons into a dangerous chasm between moving tectonic plates for nefarious purposes?

A mysterious dolphin in a sophisticated electronic harness zaps all the Rover's power. Ant and Fontaine manage to remove the harness, but can they rehabilitate this cybernetic dolphin to survive in the wild?

Mad Madeline steals the dangerous Sceptre of Queen Dorius.

The Nektons help locate a legendary Singaporean glass cabinet. However, they discover it is guarded by a terrifying and familiar creature.

The Nektons are busy recovering sunken shipping containers, so when Bethany the fish finds herself in danger, only Jeffrey can save her.

Ant has created a clever machine to clean up a vast oceanic rubbish dump. However, when the machine is been eaten by a huge creature, it's up to the Nektons to save it.

Ant and Fontaine discover the secret of the Bajau Laut people, a tribe of sea nomads living in the South China Sea. The pair are determined to help them - but how do you find a fish that walks?

Fontaine is amazed when Smiling Finn tells her that he has detected a signal from her grandparents’ missing submarine. Is this a joke, an elaborate scam, or something even more amazing?

A submarine is trapped in an astonishing location. The Nektons launch an elaborate and dangerous rescue mission to save the people inside. Could it be their missing grandparents?