Upside Down World by Amanda White

When Charity's health starts to decline, she moves in with her sister Marvel. A long-time itinerant, Charity brings little with her but her memories and a few trinkets.

Outside the house, the sea pulses in and out. Charity settles into the room Marvel has cleared for her. As best she can, she holds onto her recollections of the past and family.

The days pulse in and out like the sea.

While on the surface, Marvel's invitation seems generous and good, what lies beneath it might not be so innocent.

For, as the lines between what Charity remembers, knows, and can evaluate for herself not only blur but, too soon, begin to disappear, Marvel's quiet obsession over a childhood event pulses (more insistently than the sea and more quickly than the days) with something not exactly quiet and not quite harmless.