Two families join forces for a sailing holiday, but while Maarten and Femke are keen to spend time together, their children start arguing before they even get onto the boat. Meanwhile, trainee Michiel joins captain Arend on his trawler.
Arend finds it difficult to get his mysterious cargo aboard without being seen. Bauke is startled when he sees the skipper's gun, but keeps it to himself. Meanwhile, Isis looks forward to seeing the release of Rob, the seal she has adopted.
Femke discovers that they have drifted off course and with the navigation equipment not functioning, she no longer knows where they are. When they get stuck in shallow water, Maarten and the kids take a dingy to explore the mudflats.
Maarten tries to retrieve the dingy and returns to Femke on the boat. Meanwhile the children are waiting on the flats and argue about what they should do as the water starts rising.
Michiel is puzzled that his phone has no signal, but Arend simply laughs at him. Anne and Bo explore a little of the island and realize that it's not Schiermonnikoog as they had expected.
Having spent the night on the island, the children are hungry and thirsty. Femke and Maarten argue about whether it's best to search for the marina by boat or to return to their children by land.
The children start looking for food and fresh water on the island. Maarten sprains his ankle while he and Femke cross the dunes looking for their kids. Michiel becomes more curious about what Arend is doing.
Arend gets a call on the radio, ordering him to investigate the stranded boat, but Michiel refuses to break in to the cabin to discover more about it. While searching for food, Bo and Isis find Femke's scarf.
Knowing that their parents must be close by on the island, the children build a large fire to provide a signal for them. But without Jip's magnesium strip, lighting the fire proves difficult.
Arend is not happy when Michiel eavesdrops on his radio conversation. Feike is proud to have caught a fish, but they still have no fire to cook it. Maarten finds Jip's magnesium stick and knows they are on the right trail.
Arend is instructed to search the boat, and this time he breaks in to discover who the owners are. Femke becomes increasingly desperate that they haven't yet found their children. Everyone on the island feels the ground suddenly vibrate.
Maarten thinks that the vibrations were from an earthquake on the island. Bauke and Feike become lost and cannot find their way back to the others. Jip finds a rabbit caught in a trap.
When Jip and Feike release the rabbit from the trap, they see a strange man in the forest. While the kids argue about whether or not to eat the wounded animal, they suddenly realize that Isis has disappeared along with the rabbit.
Isis discovers a hidden bunker where she and the rabbit shelter from the storm. Suddenly, Maarten gets a signal on his phone again, and calls Bo immediately, but they only get to speak briefly before being cut off again.
Isis meets a strange man who appears to live in the bunker. Although he seems friendly, he is very reluctant to talk to her. An exhausted Maarten and Femke are finally reunited with their children - except Isis who is still missing.
Jip and Bo search for Isis and assume that she's been kidnapped, so Jip attempts to overpower Ritsaert. Michiel is curious about what Arend has been doing, but the skipper is very secretive and sets Michiel back to work.
Isis is happy to see her family again and tells them what Ritsaert had said about the dangers of the island. Femke is also keen to leave the island as soon as possible, but then they discover that their boat is gone.
The family try to work out a plan to get off the island without a boat. While searching for food, Maarten meets Arend who offers to take the family back to the mainland. But Baukie recognizes Arend from the harbor and remembers his gun.
While Arend is on shore, Michiel discovers what is in the mysterious crates on the trawler. Isis suggests that they ask Ritsaert for help getting off the island, but finding him may not be so easy.
Femke and Maarten tell the children that Femke is pregnant, but Bo takes the news particularly badly. While searching for Ritsaert, Maarten comes across a toxic waterhole. Bits orders Arend to get the family off the island immediately.
Bo, Isis and Maarten find Ritsaert's bunker and wait for him there. Bits becomes suspicious of the visitors to the island when he discovers that Maarten's a geologist. Joy and Sophie are worried that Bo hasn't arrived on Schiermonnikoog.
Ritsaert explains that Raptor is drilling for rare minerals on the island, without permission, and that it is likely to cause a massive environmental catastrophe. Femke becomes ill after eating poisonous berries.
Ritsaert wants to be left alone and refuses to help the family. When Michiel takes Arend to the island, he also sneaks on to the beach to leave some food for the family. Joy and Sophie discover that Bo's horse is lame and will be put down.
Joy and Sophie become increasingly worried and upset that they cannot contact Bo to tell her about her horse. The raft is finished and the family are ready to set off, but Michiel is sent by Arend to collect them in his boat.
When the children manage to knock the drone out of the sky and disable it, Bits sends all his men out on foot to find them. Ristsaert collects his research and prepares to leave the island, fearing he'll be discovered.
The children narrowly escape being captured by Raptor's men. Ritsaert reluctantly agrees to help the family prepare to leave the island by walking across the shallow waters of the Wadden Sea.
Ritsaert shows the children where Raptor's supply bunker is, but an alarm goes off when they try to raid it and they have to flee. The family start their crossing of the shallows, while the Raptor men continue to search for them.
When he discovers that Femke is pregnant, Ritsaert refuses to allow them to continue the crossing. Michiel tries to leave when they visit the mainland, but Arend has other plans for him.
Ritsaert's laboratory is discovered by Bits, who believes it to be Maarten's as he doesn't know that anyone else is on the island. Back on the island, Isis suggests that they must take action to save the seals and the environment.
Anne fixes the drone's camera to trick Raptor into thinking it's working without revealing their location. Isis sends a message in a bottle, including a sample of the poison, while Jip and Feike discover Raptor's communications center.
Arend is once again ordered to capture the children and bring them to Bits, but Michiel is now working against him. Jip and Anne sneak into the communications bunker and learn of the dome that hides the island from the outside world.
Femke and Maarten get annoyed that the children seem to have so little interest in helping to build the raft. Bo and Isis discover that there has been another toxic leak spreading more poison across the island, and Ritsaert gets sick.
Bits is furious that the drilling rig is broken and sends Arend to the mainland to collect an expert to help. Bo sets the raft on fire so that their parents cannot force them to leave the island before putting their plans into action.
Maarten and Femke uncover their children's lies and learn of the sabotage plan. When they go to the communications bunker to try to get help, Maarten and Femke are captured.
Isis turns to Ritsaert for help and discovers that he is sick. Michiel learns how the dome works to protect the island. Jip and Anne sneak into the bunker in search of their parents.
When Arend and Michiel are tasked with transporting Femke and Maarten across the island, Michiel tries to liberate the prisoners but is caught. Bits is furious because the problems with the drills are still not resolved.
Maarten is forced to start work repairing the drill, after being interrogated by Bits who still thinks that Ritsaert's laboratory is Maarten's. The children start making plans to try to rescue their parents.
Bauke and Feike are captured. Bits receives a call demanding double the production, so he increases the pressure to fix the drill, ignoring the risk of an environmental disaster.
The children capture one of Raptor's men and using his clothes and security card, Anne sneaks into one of the bunkers. Maarten discovers that Bauke and Feike have been captured and has to continue working for Bits to ensure their safety.
An increasing number of sick seals are being found in the Wadden Sea, and further from the island. Isis is left guarding the captured Raptor man, but when he promises to help them if released, she believes him.
The children are discovered and imprisoned with their parents. Ritsaert runs out of medicine as his sickness continues to get worse. Arend suggests a plan for Michiel to escape.
Maarten tries to explain to Bits how much damage the poison is doing, but Bits is determined to repair the equipment and continue the drilling. Maarten refuses to work unless Femke and the children are first taken safely to the mainland.
Fearing for Maarten's safety, the children steal Arend's boat to return to the island. Femke objects, until she overhears Bits on the radio and realizes how ruthless he is. Ritsaert allows himself to be captured.
Bits instructs Maarten and Ritsaert to work together fixing the drilling rig. Joy and Sophie decide to take the horse to Bo's mother and ask her for help. Maarten is impressed when he learns the children have returned.
The children put their plan into action very early in the morning, but it does not go as smoothly as they hoped. Jip, Anne and Bauke are caught in the communications bunker, and Bits is able to restart the dome.
Isis finds Michiel while she is visiting the seals, and agrees to help him. Maarten and Femke discover a bomb in the bunker while they are working to sabotage the drilling rig.
Bits attempts to flee the island, but Arend stops him and forces him to help disarm the bomb. Feike helps Ritsaert to disable the drills, and the whole family are finally able to return to the mainland.