The thunder crashed and boomed, drowning out the sound of the engines and the sharp cries of fear from the passengers. And then the cabin was lit up by the flash of lightning – so bright it hurt their eyes. Jagged bolts of electricity crackled and fizzed as they speared the roiling black clouds as if in search of the plane. Never had Sarah felt so small, insignificant and vulnerable in this metal box being tossed about by the elements thousands of feet above ground.

Her pulse was racing and she gripped the armrest as the plane bucked and juddered, then dipped and rose with alarming and stomach-churning frequency. And then it began to slowly descend, the pilot guiding it below the storm clouds and into clearer skies.

But the respite was short-lived and soon they were plunged back into darkness, with momentary flashes of lightning as the thunder growled and boomed. It felt to Sarah as if Thor himself was beating the fuselage with his war hammer, and the awful noise filled her head, reverberating right through every part of her body until nothing else existed.

She began to tremble, and the fear she’d been holding back threatened to overwhelm her. She and Jane were about to die. They’d never see their mother again. Never know what had happened to their father and Philip.

‘I’m sorry,’ shouted Jane over the noise, reaching for her sister’s hand to grasp it tightly. ‘I should never have risked this. If we die today, I want you to know that I love you, Sarah.’

Sarah squeezed her fingers and gave her a strained smile. ‘We’re not going to die,’ she said, despite her belief to the contrary. ‘The pilot will get us through this.’

‘You’ve got more faith in him than I have,’ said Jane, grimly clinging on as the plane suddenly plunged and rocked in the maelstrom. ‘I promise you one thing, Sarah. If we get out of this alive, I will kiss that pilot and I don’t care who sees me.’

Despite her terror, Sarah couldn’t help but smile at her younger sister’s defiant declaration. This was the Jane she remembered from Malaya, who acted on impulse, was childlike in her eagerness to make everything all right, and who dared to speak her mind. Not the self-assured young woman who’d returned from her secret wartime posting with aplomb and a steely determination to live her life as she pleased.

The plane was flying more evenly now, and although Sarah could see the rolling, storm-filled clouds above them, there was land beneath – a barren red land with ribbons of silver glinting amidst the scudding shadows of the overcast sky, and huddles of settlements formed from ochre-stained adobe within the soft folds and jagged promontories of a harsh and unforgiving landscape.

Flashes of sheet lightning and rolls of thunder continued to accompany the plane as it slowly approached the urban sprawl of Calcutta. Flying low over the city, Sarah and Jane could now see the sights that had been described in the guidebook they’d bought in London.