Drums of Autumn by Diana Gabaldon
Claire Randall's first unexpected trip to the past led her into the arms of an 18th century Scottish warrior named Jamie Fraser. Now they are happily reunited, but Claire has left someone behind in the 20th century---her and Jamie's daughter, Brianna. Brianna has fallen in love with a Scottish historian named Roger Wakefield MacKenzie, a man who also has ties to the same mysterious stones that led Claire to Jamie. As Roger is helping Bree research what has happened to her parents, he stumbles upon a disturbing discovery he is determined to hide. Unbeknownst to him, Bree has uncovered the information herself. It leads her to the stone circle known as Craigh na Dun, resulting in Bree plunging headfirst into the past to meet the father she never knew, setting off a chain of events that could leave her stranded forever ... or perhaps just where she was always meant to be.
Book 4 in the Outlander series. 880 pages.