Potem ko so ga zalotili pri kraji, Andyja skupaj z mlajšim bratom Markom pošljejo na skrivnostni otok, da bi preživela poletje pri stricu. Fanta kmalu odkrijeta, da je bil lastnik otoka njun ekscentrični dedek, ki je skril ogromno bogastvo in pred leti izginil brez sledu. Ob raziskovanju zgodovine otoka brata začneta odkrivati namige in skušata razvozlati uganko, povezano z nepredstavljivim bogastvom. Andy in Mark upata, da bosta še pravočasno uspela najti zaklad ter tako rešiti svojo družino.
After making one mistake too many, troubled youth, Andy Walton, finds himself with his back to the wall. Sent to live with Uncle Trent, a reclusive relative whom he has never met, Andy has to spend his summer vacation along with his young brother, Mark, at a weather-beaten cabin located in the heart of a remote island. But there, the boys become intrigued by the mystery surrounding the unaccountable disappearance of their eccentric and supposedly wealthy grandfather, who, unfortunately, has taken with him the secret to immense riches. Now, as the amateur investigators delve deeper and deeper into the past of their family and the island, they follow a faint trail of clues that could lead to a treasure: the grand prize others have already set their sights on getting their hands on it first. Can Andy and Mark unravel the secret of the lost fortune?