A young American man, Richard (Leonardo DiCaprio), travels to Thailand. During a stay on Khaosan Road in Bangkok, he meets a mysterious man named Daffy (Robert Carlyle), who tells him about a secret beach paradise. Richard then heads for southern Thailand in search of the island. Along the way, he is befriended by a young French couple, Françoise (Virginie Ledoyen) and Étienne (Guillaume Canet), and he shares the secret of the island with them.

The three then strike out across the water with inflatable bags and whatever they can carry. They reach the island, where they find a huge marijuana plantation. Heading further inland, they eventually find the hidden beach, where a small, suspicious clan of Western travellers has settled, and is led by a strong-willed woman, Sal (Tilda Swinton).

The three newcomers then struggle to find their place in the Utopian community.