'Help me, please help me.' It was a young woman's voice, pleading with him. He opened the door, certain that this was the biggest mistake of his life, and there she was, a feral creature in dirty clothes, with hollowed cheeks and scabs on her cracked lips. She told him her name and why she'd broken into his flat. Her young friend had died three years ago, she said. Her body had been fished out of the sea off the Argyll coast. She begged him not to call the police. 'There's no-one else I can go to.' It's not the only unexplained death haunting Cal McGill, a part-time PhD oceanography student with a macabre interest in floating corpses. Severed feet are washing ashore on Scotland's beaches and for some reason McGill wants to know if they're wearing trainers. The answer could make all the difference between accident and murder. Then there's the tragedy of his grandfather who was lost at sea, the mystery which sparked his childhood fascination for tracking flotsam across oceans, the mystery he's never been able to solve.