An echo in the bone - Diana Gabaldon

Two hundred years separated Highlander Jamie Fraser from wartime nurse Claire Randall. They still found a way to be together. Now the year is 1777 and finally the future is threatening to catch up with them...

With the American rebellion growing in intensity all around them, Jamie and Claire know that being on the winning side is no guarantee of safety. Making their way back to Lallybroch to fulfil a family promise might seem one way of thwarting fate, but in the chaos of war every avenue of escape is bristling with danger, and even the time-travelling Claire cannot foresee the tragedy that could tear her and Jamie apart for ever.

Meanwhile, in the apparent safety of the 20th century, their daughter reads Jamie and Claire's letters, breathlessly watching the unfolding of her parents' story - even as the past threatens her own family in the present...