Frank Randall believed that it was his duty to stay in his marriage to Claire and help raise her unborn child. In spite of the certain knowledge that another man fathered the child, Frank also knew that he could not sire children himself. He may not have been sure, at first, how he would feel towards a child that wasn’t his, but once she was born, Frank was smitten with Brianna and loved her as his own.
Having searched for and discovered historical records about the man Claire named as Brianna’s biological father – and having potentially found out other as-yet-unknown truths about the dangers of being a time-traveler – Frank took certain steps toward preparing Brianna for a possible foray into the past, including teaching her to ride a horse and to shoot. Brianna was totally unaware of Frank’s motives until she found a letter from him addressed to her, years after his death. 
When Brianna meets Jamie in 1769, after a perilous journey of thousands of miles and two hundred years, she feels joy in the initial « honeymoon » phase of their relationship, but soon struggles to accommodate Jamie’s 18th-century attitude toward marriage and responsibility.
Brianna meets Roger in Scotland while on holiday with her mother, who had been acquainted with Roger’s late adoptive father. She flirts casually with him, and they kiss after a couple of weeks of performing historical research together. After they witness Gillian Edgars’ harrowing escape through the stones at Craigh na Dun, and later the departure of Brianna’s mother through the stones, Brianna feels even more closely bonded to Roger through their shared, secret knowledge and experience.
Bearing the burden of her own experience of her parents’ marriage, Brianna refuses Roger’s first marriage proposal, knowing and fearing that even two people who seem to love each other can hurt one another in irreparable ways. Once she finds evidence in historical documents that her mother did find Jamie Fraser, but that they would perish in a house fire in 1776, Brianna withdraws from communicating with Roger and ultimately travels to the past without telling him, in order to warn her parents.
Months later, and after a long sea voyage, Roger finds Brianna in Wilmington in 1769, and she is at once overjoyed and disturbed to see him, believing that Roger’s presence in the 20th century would have been her assurance of being able to return, by using him as a focal point. Declarations are made, and they agree to be handfast – that is, married by mutual agreement but not a priest, a spoken contract that would expire after a year and one day. They spend the night together, but Brianna is furious when she learns that Roger had found out about Claire and Jamie’s deaths by fire and kept it from Brianna. They part ways, and do not see one another for almost a year, by which time Brianna has given birth to a son who may be Roger’s, but may also be that of Brianna’s rapist.
Ultimately, after learning of Brianna’s child and the circumstances, Roger returns to her and vows to raise her son as his own regardless, if she’ll accept him. They are married in a ceremony at the Gathering at Mount Helicon in autumn of 1770.
Brianna meets her younger cousin Ian Fraser Murray in September 1769, after her travel through time and across the ocean. They quickly become friends.
In October, Brianna’s handfast husband Roger MacKenzie comes to the Ridge, but due to a gross misunderstanding, Jamie and Ian believe that he raped Brianna. They capture Roger, not knowing his true identity, and give him to the Iroquois.