After giving up the search for Jamie and returning from Scotland, by December of 1968, Claire has resumed her life in Boston as a surgeon with her colleague Joe Abernathy. After hours, Joe asks Claire about her time in Scotland and guesses that what kept Claire over there for so long was some kind of relationship with a man, which Claire confirms. When Joe asks what happened, Claire is only able to offer cryptic explanations about their going their separate ways.
Meanwhile, Brianna is finding it difficult to resume her life as a student at Harvard. Confronted by her history professor that she is failing all her classes and is danger of flunking out of school, Brianna seems unperturbed by the prospect.
With this backdrop, Roger MacKenzie arrives for a surprise visit at Claire and Brianna's home, only to find the two women in the middle of an argument over Brianna's intention to leave Harvard and move out of the house. Claire pleads with Brianna to reconsider, but Brianna insists that she's tried to pick up where she left off before learning the truth about her parentage, but finds she can't and angrily storms out of the house. Clearly uncomfortable, Roger apologizes for arriving unannounced and offers to leave for his hotel, but Claire insists that he stay with them.
Over dinner, Claire asks Roger about his motivations for coming to Boston. While he offers explanations of being lonely at Christmas without the Reverend and wanting to experience an "American Christmas," it becomes clear that Roger is interested in spending more time with Brianna. Both talk about their past Christmas traditions; Roger and the Reverend delivered presents to needy children and sang carols, and Claire and Frank read "A Christmas Carol" to Brianna.
After dinner, Roger pours Claire a whisky and tells her that he does have some good news, reporting to a stunned Claire that he believes he's found Jamie. He produces a copy of a news article published in 1765 in Edinburgh that quotes lines by Robert Burns. Claire dismisses the article, suggesting that anyone could have known Burns' poem, but Roger points out that Burns wouldn't write the poem until 1786, and only somebody with knowledge of the future could have known the quotation. Finally, Roger refers Claire to the name of the publisher, Alexander Malcolm – Jamie's middle names – as confirmation that Jamie is alive and living as a printer in Edinburgh in 1765, which is only a year in the past of their shared timeline.
Claire reacts to Roger's news with an edge of anger, stating that she didn't ask him to continue searching for Jamie and was content to let the matter rest. Surprised and confused, Roger points out that Claire can return to the 18th century and reunite with Jamie, to which Claire responds that Brianna needs her mother and she can't leave her. Chastened, Roger asks how he can help and Claire asks him not to say anything to Brianna about his findings.
The following day, Claire finds Joe studying the skeletal remains of a woman found in a cave in the Caribbean by an anthropology colleague. To Joe's surprise, Claire quickly surmises that the remains belong to a 150-year-old murder victim, a fact which Joe confirms upon examination of a bone from the neck, which is nearly cleaved through and indicates that the victim had her head nearly cut off. Further examination also confirms that, although the anthropologist originally assumed the bones belonged to an African slave, they are actually those of a Caucasian woman. When Joe asks Claire how she could tell so much just by looking at and touching the remains, Claire dismisses it as intuition.
Conversation turns back to talk of Claire's mystery man, which she confides to Joe is Brianna's real father. Joe finds the revelation explains a lot, pointing out that Claire and Frank were never really happy together. Joe pointedly asks Claire if she is still in love with this man, and Claire admits that she never stopped loving him. Joe urges Claire to pursue a relationship with this man again, that she deserves to be happy. Claire protests, insisting that Brianna is still struggling with the truth about her father and that she can't leave her, but Joe believes that Brianna will come around.
Meanwhile, back at the Randall house, Roger and Brianna catch up over an episode of “Dark Shadows”. Roger whimsically talks of sampling lobster rolls and Boston cream pie as part of his American Christmas experience. Brianna tells Roger that Harvard is having a ceremony to create a fellowship in honor of her father and asks Roger to accompany her, and Roger agrees.
Prior to the ceremony, Brianna and Roger wander through the cloisters and Roger's musing on the history of the place turns to personal history. Brianna draws parallels between her own personal revelations and the tendency of the historical record to be biased or flat out incorrect. Roger explains to Brianna that he never knew his parents, but shares a story the Reverend told him about his father that helped make him a real person in his imagination. Brianna points out that the story the Reverend told him may not be true, but Roger insists that the verity of the story didn't matter as long as the connection was real. Brianna seems unconvinced.
Later, after the ceremony, Claire is confronted by Sandy Travers, Frank's longtime mistress, who berates Claire for not letting go of Frank and accuses her of being selfish. Sandy confides that the reason Frank never left Claire was because part of him still loved her, and that she resents Claire for forcing her to share Frank for almost 20 years. Sandy leaves Claire clearly shaken, which Brianna observes from across the room.
Afterward, Brianna asks Claire about Sandy and how she knew her. Brianna says that she recognized the woman from when she was younger, that she had seen Frank speaking to her and noticed that Frank looked at her the same way he used to look at Claire. Claire confirms that Frank was in love with Sandy and was intending to leave Claire to marry her. Brianna speculates that given her resemblance to her birth father, Frank must have resented her as she was a constant reminder that she wasn't his daughter. Claire vehemently assures Brianna that Frank loved her very much. When Brianna asks Claire if she resents her for having to leave Jamie, Claire tells her she resented having to leave, but never blamed Brianna for it and reaffirms her love for Brianna. Claire then confesses Roger's revelation that Jamie is still alive and her resolve to stay with Brianna in the present, prompting a protest from Brianna, who claims that she is grown up and can take care of herself.
On Christmas Eve, Claire, Joe, and the rest of the hospital staff watch the historic Apollo 8 broadcast from lunar orbit. Joe wonders aloud whether somebody could come back from a trip like that one and remain unchanged. Claire stares out the window at the night sky, likely contemplating her own life-changing journey and beginning to consider the possibility of reuniting with Jamie.
Later Claire talks to Brianna about the implications of her returning to the past to reunite with Jamie. Claire explains that once she's gone, she may never be able to return, that there is no guarantee that they will ever see one another again. While this possibility seems to give Brianna pause, she still urges her mother to follow her heart and asks that she tell her father everything about her. Finally, Claire shares her insecurity about whether or not Jamie will have forgotten or moved on from her.
The following day at the hospital, Claire asks Joe for a second opinion. When Joe inquires as to the identity of the patient, Claire qualifies that she needs an honest opinion from a male perspective, asking Joe if he thinks she is sexually attractive and whether she has changed much over the years. Joe asks if she's thinking about reuniting with her lover from her past and Claire confesses that she's ready to give life with him another try. Joe tells Claire that she's a "skinny white broad with too much hair and a great ass", and assures her that her man will be more than satisfied with her. Self-conscious but pleased, Claire thanks him and Joe wishes her well.
That evening, Claire, Brianna, and Roger exchange Christmas gifts. Brianna and Roger give Claire some vintage coins that they found in an antique shop and a book of Scottish history. Brianna also gives Claire a necklace with a topaz setting, Brianna's birthstone, to assist with her passage through the stones at Craigh na Dun. Claire also confesses that she has "borrowed" some surgical tools and a stock of penicillin from the hospital to take along with her as well. When asked how she plans to carry everything, Claire explains that she will have to make an outfit of some kind, prompting Roger to remark that she'll need a Utility Belt like Batman, eliciting a snide retort from Brianna that he's been watching too much television.
Claire spends a few days assembling a vintage outfit, complete with secret pockets to hold her modern tools, dubbing it "the Batsuit". Ready to leave, Brianna asks to accompany Claire to Scotland to see her off, but Claire insists that she wants to go alone, that having Brianna there would break down her resolve. Claire gives Brianna her resignation from the hospital as well as the deed to their home. The three share a teary final goodbye and then Claire boards a taxi to the airport.
Now alone, Roger asks Brianna if she's alright. Brianna tells him to wait, as which point she goes to the kitchen and, after donning a Santa hat and putting on a brave face, comes out with a platter of lobster rolls and Boston cream pie, much to Roger's delight. Roger then tells Brianna that he has a gift for her as well and hands her a present from under the tree. Briana opens it to find a copy of "A Christmas Carol", which brings a smile to her face. The two share a kiss, then snuggle up together on the sofa and Brianna starts to read.
Claire arrives at the airport and as she steps from the cab the scene cuts to 1766 as she steps out of a carriage onto the streets of Edinburgh. Claire stops a boy in the street and inquires where she might find a printer named Alexander Malcolm. The boy points her down the street, directing her to Carfax Close, and as Claire arrives she sees the sign in front of the shop reading "A. Malcolm". Tentatively, she climbs the stairs to the door and after a pause walks in, the door sounding a bell to announce her presence. Claire looks around but the office appears empty, then suddenly she hears Jamie's voice carrying from the back, asking, "Is that you, Geordie?"
With a look of anticipation, Claire follows the sound of Jamie's voice to the landing overlooking the print floor, where she spots Jamie at work with his back to her. "It isn't Geordie", she responds, and Jamie's back tenses with recognition. "It's me, Claire." Slowly Jamie turns around and his face turns to stunned bewilderment. Claire smiles at him, teary-eyed, and Jamie collapses to the floor in a dead faint, to Claire's great shock.