Alba arrives in Rhodes, a small fishing village, to spend the summer at her aunt Helena's house. She thinks it will be a boring and lonely summer... she couldn't be more wrong. She will soon make wonderful new friends: Lucas, Sali, Olivia and Nil. Together they will make an extraordinary discovery: they will find a gold coin from Roman times. This finding will lead them on the trail of a treasure. Along the way they will come across dark powers that will try to make them fail. Powers headed by Nina, with the mission of building a luxury development in the town and willing to steal the treasure from them. But the Argonauts, far from giving up their fight to save the history of Rhodes, will face dangers and overcome failures without ever giving up. And as they join forces, they will make their greatest discovery: their friendship is far stronger than all the obstacles they may encounter in this unforgettable adventure of the Argonauts.