Claire Randall has returned to her own time, where she has been living for 20 years with her husband Frank. Following his death, she brings her daughter, Brianna, to the home of the Randalls' old friend, Reverend Reginald Wakefield. There, Claire hopes the Reverend's adopted son, Roger, can help her discover what happened to the men of Lallybroch after the Battle of Culloden.
Roger, using his Oxford credentials to obtain information, finds proof that the men of Lallybroch returned home safely. He accompanies Claire and Brianna to an old churchyard, looking for the grave of Jonathan Randall, Frank's ancestor, but also finds Jamie Fraser's gravestone: it is part of a "marriage stone", showing Claire's name but no date. Claire reveals Brianna's true paternity to her and Roger. Brianna angrily denies her mother's story, but Roger is fascinated, and Claire recounts her time after the events of Outlander .
At the end of Outlander , Claire has convinced Jamie to stop the Jacobite risings and the consequent slaughter. After learning that Charles Stuart is trying to get money from the French king Louis XV to fund the Jacobite cause, they travel to Paris, where Jamie uses his cousin Jared's wine business to gain the aristocratic connections necessary to plot against Stuart.
A French boy named Claudel, brought up in a brothel, helps Jamie flee some thugs, so Jamie adopts him as his foster son and renames him Fergus. When Jonathan "Black Jack" Randall arrives, Jamie, despite a promise to spare Randall's life to protect his descendant Frank (Claire's previous husband), challenges Randall to a duel, and renders him impotent. Claire miscarries and is taken to the hospital. Jamie is sent to the Bastille for dueling.
Claire frees Jamie by an arrangement with King Louis XV of France. Back in Scotland, they settle into farm life at his home at Lallybroch with Jamie's sister Jenny and her family. Jamie receives a letter from Stuart, announcing his attempt to retake the throne of Scotland, and gathers the men of Lallybroch to join the Stuart army. Young Lord John Grey, an English scout, stumbles upon Jamie and Claire. Thinking Claire a prisoner, Grey tries to "save" her, whereupon Jamie breaks the boy's arm but spares his life. Information gleaned by Jamie from this encounter helps the Highlanders win at the Battle of Prestonpans; but the Rising still fails at the disastrous Battle of Culloden.
Claire discovers that she is pregnant again. Jamie and Claire discuss assassinating Stuart, but decide against it. Dougal MacKenzie, having overheard their conversation, accuses Claire of persuading Jamie to betray his people, and attempts to kill Claire. Dougal is stabbed and dies in Jamie's arms. Jamie, knowing that the Jacobites lose Culloden, forces Claire and the unborn Brianna to return to her own time to spare her the battle's aftermath, and returns to Culloden, intending to die in the battle.
Claire relates that she had returned to Frank, who disbelieved her story but insisted on helping her raise Brianna, and asked that she would only tell Brianna the truth after his death. Upon hearing it, Brianna refuses to believe Claire's story. Claire enlists Roger's help by revealing him as the descendant of Dougal MacKenzie and Geillis Duncan. Claire admits to Roger that while hiding in the caves of the Highlands, awaiting Jamie's release from prison (as told in Outlander ), Dougal had delivered a message from Geillis that read: "I do not know if it is possible, but I think so" and the numbers 1,9,6 and 8. Claire deduces that these signify the year 1968, and Claire and Roger suspect that Geillis was telling her the year of her own time travel. Claire, Roger, and eventually Brianna witness Geillis Duncan/Gillian Edgars' disappearance through the stone circle at Craigh na Dun after murdering her husband, Greg. Roger informs Claire that Jamie did not die at Culloden.