In summer, Annecy would be teeming with tourists enjoying the crystal-clear waters that fed the lake from mountain streams and snowmelt, and snaked through the old canals that cut between the town’s narrow stone arches and passageways lined with cafes and market stalls. But now it was too cold for anyone but locals and a few travellers passing by on their way to the last of the season’s skiing higher up in the Alps.

Just the locals, the skiers, and a woman called Anna, who was standing on the high diving platform at the Plage de l’Impérial on the edge of the lake.

She looked like she belonged up above the water, wearing a maroon one-piece swimsuit with her long hair tucked under a black cap. The fine features of her face were calm, composed, seemingly unaware of the icy wind that was picking up and sending ripples across the surface of the lake ten metres beneath her.

The Plage was closed. It was a victim of the dwindling fortunes of the hotel next to it, which had tried and failed to bring the glamour of Monaco to the mountains and had shut down permanently after the last summer season. However, it had taken Anna a considerable amount of effort to negotiate her few days of rest and recuperation with her employers, and she was going to spend them doing exactly what she wanted. So, for the last two evenings, just before sunset, she had picked the simple lock that had been chained across the gates of the Plage, changed into her swimsuit, and practised her diving.

She craved the cold, the feeling of it wrapping round her and numbing every inch of her skin. She stood perfectly still on the diving board, breathing slowly through her nostrils to suck the chill deep down into her. Then she raised her arms, sprang off her feet and jumped into a graceful arc that took her into the brutal, brief oblivion of the freezing lake.

When she broke the surface again and gasped air back into her lungs, she floated in the water for a moment and looked across the empty pontoons that lined the lake and would fill with rowing boats and pedalos once spring finally arrived, towards the Jardins de l’Europe with its lawns and flowerbeds that were kept pristinely manicured all year round.

She saw a man in a heavy coat leaning against the wrought-iron railings of the Pont des Amours on the edge of the park staring at her. She held up both her arms, flailing as if she was drowning. Then, when she saw the man tense upright, she threw her head back, let out a loud laugh, and started swimming with deep, even strokes back to the diving board.

Five minutes later, Anna had dried herself off and changed into a thick jumper, trousers, and her own winter coat.