It’s midsummer when Paul arrives on the island in the heart of the Mediterranean sea to which he has been invited by Gaia, a spirited young actress. A shadow hangs over the young man, and Gaia senses that it hides a greater secret than the success of Sirena, the graphic novel which exhausted his creative streak. The days that follow are filled with passion and inspiration thanks to the magic of the island, which the natives call Issa (She), almost as though it were alive. “Issa gives, Issa takes,” repeats old Maria enigmatically, while the holiday is marred by accidents, grief and disappearances. Wherever he ventures, Paul finds himself increasingly drawn to something unspeakable which takes shape in the form of a young woman he sees on the rocks by the sea one night. She is the double of the only girl he ever loved - and lost: Nadja. It seems impossible… Until a charismatic old man tells him that it was she, that mysterious creature, who saved him when his plane was shot down off Issa in 1943. A fascinated Paul follows his siren to discover what awaits him in the abyss – both the one at the bottom of the sea and the one he carries within himself.