It was quicker if both people were moving but she had no choice. The other side of the water was twenty yards away, maybe less. She rolled her trousers down, her hands shuddering in the water, but the material was painfully thin. Why didn’t I wear jeans? The lionfish’s fins were stiff, needle-sharp spears. If threatened, or distressed, which it surely was, Hemingway would shudder violently near any perceived danger, making sure its spines disabled the potential predator. Georgie’s body would react instantly to the neuromuscular toxins in the venom. Her immune system would go into overdrive, flooding her body with histamine. Her lungs would swell, breathing would become almost impossible and she might even have a seizure.

Fox was right: if she toppled over, paralysed, she would drown in less than a minute.

‘Come on, move!’ she commanded herself.

A small splash nearby stopped her and almost sent her into meltdown. It had been a few feet away, no more. A fin breaking the surface of the water, heading towards her? Oh my God, oh my God! Trembling, she thrust the pitiful phone light in the direction of the noise but she couldn’t see the water round her legs let alone any further.

She thought about running, kicking her way through the water. It was surely her best hope.

Then another noise aroused her attention. The sound of the door at the top of the stairwell opening and a light splashing off the brick wall.

‘Georgie?’ called a voice.

Her heart skipped several beats. Could it be?

‘Li!’ she called out.

There was a scraping sound as Li negotiated the stairs. ‘What the fuck are you doing down here?’ Her flatmate was half laughing, oblivious to the danger she was in.

‘There’s a light switch at the bottom of the stairs, on the left!’ Georgie shouted.

A few excruciating moments passed before the bulb spluttered into life and Georgie saw Li looking around the basement in awe, then seeing Georgie at the far end, the water up to her waist. Her expression changed from amazed to confused.

‘Is this a public pool?’ Li asked. ‘Only I forgot my bikini.’

‘There’s a lionfish in the water!’ Georgie blurted out. ‘It’s a bit bigger than the size of a small football and white with black stripes and lots of fins. I need to know where it is so I can get out!’

Li hesitated, blinking as she processed the information and for a second Georgie thought she might burst out laughing, assuming it was a joke.

‘My anaphylaxis!’ Georgie screamed, desperate. ‘Bee stings, remember? It’s the same if I get stung by a lionfish!’

Realisation crossed Li’s face. She dived to the edge, shining her phone’s torch light across the surface of the water.

‘Take a few steps forward,’ Li instructed. ‘Move the water around where you are.’

‘But I think—’

‘Just do it!’