The first book in the Timeless series introduces Libby Conant, a 19-year-old time-crosser who lives two simultaneous lives. Each time she falls asleep after midnight in one life, she wakes in the other. In 1774 Colonial Williamsburg, Virginia, she helps her family keep their printing press and the
Virginia Gazette running after her father's recent death. In 1914, she is Anna Elizabeth Wells, daughter of a wealthy New York shipping magnate and his socially ambitious wife. On her 21st birthday, she must permanently forfeit one life and remain in the other.
Libby's 1774 mother, Theodosia (called Mama), is also a time-crosser who chose to forfeit her 1990s life. She is Libby's only confidante about their shared gift, marked by a sunburst birthmark over the heart. Mama and Libby struggle to run the press while supporting Libby's younger sisters, Rebecca and Hannah. The family faces debtor's prison until the House of Burgesses, Virginia's colonial legislature, awards them the public printing contract. Henry Montgomery, a young assembly clerk whom Libby has loved since childhood, delivers the good news. Henry's loyalist parents severed the families' friendship years earlier because they disapproved of his attachment to Libby.
In 1914, Libby's mother, Abigail Wells (called Mother Wells), brings her to London for the social Season to marry her to a titled Englishman. Mother Wells introduces Libby to Reginald Fairhaven (Reggie), the Marquess of Cumberland, a government official with political ambitions and a crumbling estate that needs a wealthy bride's dowry. Libby's only ally is her lady's maid, Edith, whom Mother Wells threatens to dismiss without a reference if Libby does not cooperate.
As colonial tensions escalate, Henry confides that the burgesses plan to call for a day of fasting and prayer in solidarity with Boston, where Parliament has closed the port. The Conants' journeyman, Louis Preston, refuses to print the resolution, calling it treasonous, so Mama, Libby, and their household produce the broadside, a printed public notice, themselves. Governor Dunmore disbands the assembly in retaliation. That evening, Henry visits Libby and tells her she is "dearer to me than my very own life" but insists he must keep her at a distance because of things beyond his control (102).
Lord Cumberland courts Libby aggressively and declares his intention to propose. Mother Wells accepts on Libby's behalf. Aboard the ship home, Libby meets Congressman Hollingsworth, a Virginian bearing a matching sunburst birthmark; they recognize each other as fellow time-crossers. Mother Wells claims to be gravely ill, and a doctor confirms a genuine physical decline, pressuring Libby to agree to the engagement. She consents on the condition the wedding be postponed a year, but Mother immediately recovers, having already set the date for six weeks later. Father Wells cannot legally stop the proceedings because Mother signed a binding contract with Lord Cumberland.
On her 20th birthday in Williamsburg, Henry almost kisses Libby in the dark garden but pulls back. She confronts him about rumors that he is spying, and he declares he will help win independence or die trying but will not explain why he cannot marry her.
On August 1, 1914, Libby is forced to go through with the wedding, weeping beneath her veil. That night aboard the ship to England, Reggie forces himself on Libby despite her protests. When Britain enters World War I, Reggie is called to duty, and Libby is sent to Cumberland Hall, his manor in Whitby, North Yorkshire, to oversee renovations. In Williamsburg, Governor Dunmore quarters a British officer, Lieutenant James Addison, on the Conants' property as retaliation for their Patriot printing.
In December 1914, German warships bombard Whitby. Libby opens Cumberland Hall as a hospital, caring for the wounded alongside Dr. Aiken, a local physician. Reggie returns for Christmas, apologizes for his earlier behavior, but assaults Libby again while intoxicated. On Christmas Day in Williamsburg, Henry declares his love, and he and Libby share their first kiss. He insists he cannot marry her while war looms, refusing to risk making her a widow.
In January 1915, Libby discovers she is pregnant. The baby will be born after her 21st birthday, meaning she cannot forfeit 1915 without killing the child. She is now committed to this path, just as Mama was once forced to stay in 1774 by her own unexpected pregnancy. Mama reveals she chose 1774 over the 1990s for Libby's sake.
Lieutenant Addison warns Libby that the governor knows Henry is working against him and that Henry faces execution. Mama announces her engagement to a widowed cobbler and her plan to sell the press, ensuring the family will be provided for after Libby is gone.
At Cumberland Hall, Libby finds history volumes in the library that reveal Henry's fate: He was captured during the Siege of Boston on June 17, 1775, while carrying papers that exposed the Patriot plan to fortify the surrounding hills. His capture alerted the British, leading to the Battle of Bunker Hill, and he was hanged for treason on June 19, Libby's 21st birthday. Desperate to save him, Libby begs Henry not to go to Boston, knowing this will forfeit her remaining weeks in 1775. Henry agrees. Libby spends her last day with Mama and her sisters, then falls asleep in Mama's arms.
She wakes at Cumberland Hall and checks the book. Nothing has changed: Henry still went to Boston, was still captured, and was still executed. The next morning she wakes at Cumberland Hall again, confirming she has permanently left 1775. Grief-stricken, Libby resolves to live for her child.
On September 17, 1915, she gives birth to a son, Henry Theodore Reginald Fairhaven, called Teddy, who bears no time-crosser's mark. Weeks later, a telegram informs her that Reggie was killed in action in France. Now a widow controlling her fortune, Libby returns to America.
In New York, Libby confronts Mother Wells and takes control of her future. At a dinner party, she meets John D. Rockefeller Jr., through whom she learns of a plan to restore Colonial Williamsburg as a living history museum and joins a tour of the town. There she learns that Mama left a diary dedicated to her, preserved at the College of William and Mary.
Lingering beneath the elm tree in her old backyard, Libby sees a man walk through the gate with blue eyes and a stride she recognizes. It is Henry Montgomery, alive in 1916. They discover they were both time-crossers sharing the same two eras without ever knowing. Henry, who in this era goes by Dr. Hollingsworth, is a professor at William and Mary and the son of Congressman Hollingsworth. He explains that he knew about his 1775 death from reading about it in college, which is why he fought his love for Libby and why he went to Boston despite her warning: He had accepted his fate, especially after her body died the very next day. Libby realizes every painful event in her life led to this reunion. Henry asks her to marry him.
In the epilogue, set on January 1, 1921, Libby gives birth to their daughter Margaret Theodosia Hollingsworth at their restored home on the Palace Green in Williamsburg. The baby bears two sunburst birthmarks, one over her heart and one on the back of her head, combining both family lines in an unprecedented way whose meaning remains unknown, setting up the continuation of the series.