Mapping the Edge — Sarah Dunant

When Anna decides to take an impromptu trip to Italy, she packs her bag, leaves her 6-year-old daughter, Lily, at home with close friends, and steps onto the plane. She's always been a woman of action, and her personal and professional lives have been filled to overflowing recently. So her friends Paul and Estella think nothing of the jaunt--it's a well-deserved break, a weekend for psychic refreshment, a brief step outside reality.
But a disappearance? When Anna fails to return, Paul and Estella make excuses, to themselves and to Lily. When the weekend stretches toward a week, the possibility of her permanent absence becomes hauntingly real.