Helga hopes the session gave Claire something too. She certainly seems to be coming out of her shell and that timid, eager-to-please way she had about her when they first met has given way to a more secure confidence.

Today, the water is just how Helga likes it. Cold and buoyant and high. Maddy, who usually gets in slowly, strides in and dives in straight away. She tips back her head in the water with a sigh. She lies on her back, like Helga has shown her, floating on the surface like a starfish for a few moments, as the others get in.

A man is fishing off the high groyne, his lines taught and Helga can see a shoal of mackerel shimmying below in the clear water. She doesn’t tell Maddy. She doesn’t want to blow her confidence when she’s starting to love the water so much. She sets off in the opposite direction, away from the fishermen.

‘Did you know that it’s the spring solstice today?’ Tor says as they swim out.

‘So it is,’ Helga says. There’s a whale-skeleton of white clouds way above. ‘Funny to think that over in Australia their autumn is starting today. That they’re facing the dark days ahead and getting out their jumpers and coats, whilst we’re looking forward to the summer.’

Is Linus in Australia? She imagines him in a smart house with a yacht at the end of his private dock.

‘It’s the equinox too,’ she adds.

‘I like the word equinox,’ Dominica says. ‘It gets you a good score in Scrabble.’

‘From the Latin for equal, aequus, and the night, nox,’ Helga explains. ‘The spring equinox is also known as the vernal because the two hemispheres of the earth are receiving the sun’s rays equally. Did you know that the sunrises and sunsets are faster at the equinox?’

‘I love that feeling that summer is coming,’ Claire says. ‘It’s easier to have a brighter outlook when the sun is shining.’

‘Won’t it be amazing when we can get out of the sea and dry off in our costumes on the stones and lounge around in the sun?’ Dominica says. ‘Although I’ll miss the cold buzz.’

‘We certainly will,’ Helga says, because it’s true. It won’t be the same in the warmer weather, but even so, she likes the fact that this group is a constant. That it’s a given that they’ll be swimming together in the months to come.

‘Is the spring equinox the same as the spring tides?’ Maddy asks and Helga likes that the Sea-Gals are all listening in.

‘No. The spring tides happen around the new moon, or the full moon. When you look up, the moon is either invisible or you can see it, and, at that point, the moon and the sun are generally in a straight line. When that happens there’s a tidal bulge, which means that the high tides are higher and the low tides are lower.’

‘What’s the difference between spring and neap tides then?’ Tor asks.