The Siren was a three-masted schooner, with ten passenger berths and a crew of eight. Amy looked at her now, sitting serenely at anchor, her gleaming black hull reflected in the water. The yacht was perfectly at home here, and so was Amy. She had learnt to swim almost before she could walk and would sometimes stay in the water for hours on end. She had no need of a bathing cap because, to the horror of her father, she had recently cut off all her long curls and styled her hair into a more fashionable bob. She was often mistaken for a boy, but that didn’t bother her. She knew who she was.

She reached the rocks and hauled herself out to sit in the sun and warm herself. It was late May, still early enough in the year for there to be the occasional cold current in the sea.

She shook sparkling droplets from her freckled skin and looked over at the shore. A dense wood of dark green cypresses grew right down to the little sandy beach where last night they had set up tables and eaten their supper under the stars. The island, one of the Cyclades that spread out across the sea south of Athens, was tiny and uninhabited and didn’t even appear on most maps.

A diving knife in a leather sheath was strapped to Amy’s leg. It belonged to Louis, the big French first mate, and he had shown her how to prise shellfish from the rocks to eat. Around her waist was strung a net that she used to hold her catch of mussels and clams. Sitting here on the rock, she felt like a savage, a million miles away from England and her boring school. She was the happiest girl in the world and this must surely be paradise.

She heard the ship before she saw it, a dull throbbing sound, but thought nothing of it. The Mediterranean had been a busy maritime highway for centuries. She busied herself searching for shellfish, dimly aware of the engine noise getting nearer, but it was a shock when she saw a tramp steamer chug into view, pumping smelly, black smoke from its short funnel. She watched as it moved alongside the Siren and noisily dropped anchor. Amy could see several crewmen hurrying about the deck; their skin tanned dark brown by the sun, their outfits grimy and stained.

Next to the sleek, clean lines of the yacht, the steamer looked squat and ugly. Amy peered at the name on the side, written in peeling red paint – Charon.

The wind shifted, smearing the plume of black smoke across the sun and throwing the harbour into shadow. For a moment Amy, who was standing knee-deep in a rock pool, was chilled, and she shivered.

From the deck of the Siren, her father watched the arrival of the steamer with some curiosity. Other than the name, he could see no flags or markings of any kind and wondered why it had chosen to put in here, in this obscure and secluded harbour.