Alison, 39 years old, is twice-divorced, with three children, on the verge of moving in with a man called Bobby. Her breast is sore and she is afraid it's cancer. Her mother tells her it's more likely she's pregnant. She says she uses contraceptives; her mother tells Alison that she was conceived when a condom broke.

Alison considers abortion, recalling her last pregnancy. Having given birth to a child with Down's Syndrome who died at three months, she had had amniocentesis and was told that she was carrying twin boys, both normal. When the twins were born, though, one turned out to be a girl. One twin, it seemed, had been tested twice. Although the female twin did not have Down's Syndrome, Alison began at that point to worry about luck and the uncertainty of medicine (and of life).

So now, pregnant again, she asks her mother what she should do, and is told to "trust to luck." But she is afraid that her luck has run out and she must take control for herself. A scan shows that she is carrying twins again. Only now does her mother tell her that she is in fact a twin, that her sister had Down's Syndrome and died shortly after birth--in fact, her mother admits, the midwife "did away with" her. (The euphemism carries the senses both of euthanasia and of murder.)

Hearing this, Alison decides she wants to have an abortion right away. Her doctor, thinking the problem is that she wants only one child, gives her the option of selectively terminating one fetus and carrying the other one, but tells her she wouldn't be able to choose which to keep and which to abort. She rejects the idea, imagining how she'd tell the surviving twin about her decision later on, and decides instead to "have them both and trust to luck."

As she leaves the clinic, she begins to bleed and miscarries. Later her mother tells her that she, too, once miscarried twins, and tells Alison she'll have better luck next time, because of the bleeding: "Blood, " her mother says, "is the libation the God of Chance requires."