Stella Bain by Anita Shreve

Stella Bain has no memory of her past when she wakes up in a hospital bed in Marne, France.  It is 1916, and she wears the uniform of a British war nurse but speaks with an American accent.  As soon as she is able, Stella sets out for London, where she hopes to find answers.  What she discovers-with the help of Dr. August Bridge, who takes an interest in her case-both shocks and startles.  As Stella's memories come racing back, she must undertake a journey across the ocean to confront the haunted past of the woman she used to be.