She watched Brenda. She was swimming, head down, parallel to the shore. She was a good swimmer, but in a lake anything could happen. She could get a cramp, hit a rock, have a heart attack. Not likely, but possible. Then she would be gone, vanished into the depths of the lake.

And then what would Alice do? She couldn’t rescue her. And who would know? There’d be no one other than Alice to report her missing. It would be up to her to call the authorities and hand over Brenda’s belongings to them.

But Brenda would be fine. They’d have a swim in the lake and everything would be OK.

More than likely, anyway.

‘Brenda!’ she called. ‘Hold on. I’m coming in!’

Alice tiptoed into the lake. It deepened quickly and she raised her arms as the water level rose to her waist. The rocks were slippery under her feet and she had to place them carefully.

Eventually, she could avoid it no longer. She took a deep breath and dived in.

The cold took her breath away, and she held her head out of the water, hyperventilating. Eventually her body began to adjust and it started to feel comfortable, then exhilarating. She trod water, surprised at how steeply the lake bottom had shelved away.

She tilted her head back to look up at the scree slope, looming above the water’s edge. Presumably the gradient continued like that under the surface. She had a sudden feeling that she was suspended above a chasm, and could fall into it at any second. All that was stopping her from sinking into it was this flimsy, cold water. It was easy to imagine yourself sinking, swirling down into the abyss.

Brenda called to her.

‘It’s warmer over here,’ she said. ‘Must be in the sun or something.’

Alice swam towards her, breaststroking to keep her head above the water.

‘It doesn’t feel much warmer,’ she said.

‘It’s here, in this patch,’ Brenda said. ‘Maybe there’s a thermal spring or something. You get that in lakes. Called a thermocline.’

She dived down, her feet kicking as she disappeared under the water. When she came up she was gasping. ‘It’s much colder even a few feet down,’ she said. ‘But this patch on the surface is nice.’

Alice swam closer until she was no more than an arm’s length from Brenda. ‘It doesn’t seem warmer to me.’

‘Maybe I’m just getting used to it,’ Brenda said. She rolled onto her back and floated, her arms outspread. She was graceful in the water, like an otter.

‘Isn’t this amazing?’ Brenda said. ‘I’ll remember this for ever. When we’re done, can you take a photo of me? My phone’s in my day pack.’