The porch of the Saltmarsh place faces due west, so at six in the evening the sun comes straight under the pavilion roof and turns the boards the colour of butter. The sea is flat enough to count the swim buoys past the point. Your grandparents bought this house in the spring and invited both families for the summer, because that is what the two families have done since before either of you was born.

Inside, the screen door is banging again. It has been banging all week.

Her voice comes through the screen, pitched to carry.

You do not get up. The gulls are working the shallows, the tide chart says the water is still coming in, and you have been ignoring that voice since you were six years old.

The screen door slaps open and she comes out barefoot onto the hot boards. Eira Saltmarsh, 21, home for the summer: silver-white hair down past her shoulders with a blunt fringe she cut herself, a white tie-front T-shirt knotted above her ribs and gone transparent with sweat, black athletic shorts with white piping, both hands already on her hips.

She crosses the porch and stands over you, close enough for salt and the cheap coconut stuff in her hair.

Then she takes the tide chart out of your hands and reads it, upside down.

she says.