When Danger, the Roberts' pet river otter, disappears, the family desperately searches the island for the animal. In a series of flashback sequences, each of the family remembers how the otter was shot by salmon poachers and Jonah was nearly killed when his small boat was swamped by the crooks fleeing the maritime police.
While Grant is fixing dinner for Nicole and Jonah, Joyce comes by with a salmon that she bought from a couple of "hucksters." Grant determines that the sellers were poachers and sets off to investigate. On the way to the hatchery Grant, Nicole and Jonah visit their old friends, brothers Bert and Cully. The police discover illegal salmon in the brothers' storage shed which Grant suspects were planted. With Bert and Cully facing charges of poaching and eviction from their camp, Jonah and Nicole discover evidence that they hope can clear the brothers and lead the police ...
While diving at a new aquarium research facility, Jonah and Nicole discover barrels dumped into the water. One of them is leaking and an unknown substance gets into Jonah's eyes, causing painful burns. Jonah is rushed to hospital and while Dr. Kelsay works to save his eyesight, Grant sets out to apprehend whoever has been dumping toxic waste into the sea.
George sends Grant to Abbot Bay to investigate sightings of a "monster" that the locals have affectionately called Abby. Meanwhile TV host Graham Sanderson schemes to undermine Grants efforts and claim all the credit for the monster's "discovery."
Jonah's friend Dennis is about to perform a potlatch dance in honour of Chief David. Dennis receives a gift from his uncle Charlie which is a replica of a thunder bird mask on display at the aquarium. Dennis and Jonah decide that the appropriate gift for chief David would be the original mask that once belonged to his people. The boys switch masks at the aquarium, but when they present Chief David with the original mask, they are surprised at his reaction.