Dragonfly in Amber by Diana Gabaldon is the second book of the Outlander series. This book is once again, incredibly researched and fraught with Scottish history. Another one I couldn't put down!
Twenty years had passed since Claire Randall had returned to "real time". She had completed medical school and she and her husband Frank and their daughter Brianna lived in Boston. Two years after Frank died, Claire and Brianna went to Scotland so Claire could show her where Claire and Frank had gone after the war. Shortly after arriving, they went to visit Roger Wakefield, a historian. His uncle had been a friend of Frank and Claire's and had recently died. While visiting with Roger, Claire became interested in his work and over the next few weeks, Roger helped Claire discover that Jamie Fraser had not died in the battle of Culloden as she had always thought. She also got the courage up to tell Brianna about her time travel and that Brianna was really Jamie's daughter.