In June 1778, upon learning that he is in fact a bastard son of Jamie Fraser, William is deeply disturbed – he can't tell the truth to anyone, but he also can't live a lie and feels that he doesn't deserve his title of Earl of Ellesmere. He is also angry with his stepfather, who has been lying to him for years.
William meets Jane Pocock in a brothel in Philadelphia in June 1778, shortly after he learns—to his horror—that Jamie Fraser is his father. William pays to spend a night with Jane, in order to save her from a repulsive client Captain Harkness.
As the British army prepares to leave Philadelphia, William assists in the evacuation of prominent Loyalists.
He meets Denys Randall again in June 1778, during the British army's exodus from Philadelphia. He informs William that he dropped "Isaacs" from his name after his stepfather died, and advises William to avoid Captain Richardson.
On his way out of the city, William meets Ian Murray and Rachel Hunter. Adding to his anger towards Ian's uncle Jamie, Rachel informs William that she and Ian are engaged. William and Ian get into a fight, and William gets Ian arrested for assaulting an officer. William then forcefully kisses Rachel and they part company on bad terms.
Short time later, Jamie approaches William and threatens to disclose publicly his paternity if William doesn't get Ian released, and William obeys.
William lands up as an aides-de-camp to General Clinton.
Jane, a Philadelphian prostitute of William's acquaintance, asks him for protection for her and her sister Fanny.
June 28, 1778 at the Battle of Monmouth William is knocked unconscious by Hessian grenadiers. Ian finds him but is assaulted by two Indians. He then reaches Jamie and takes a few soldiers to get help for William. William is reunited with John and Hal Grey.
In early July 1778 Jane and Fanny disappear from the army followers' camp, and William goes to look for them.
Having located Jane and Fanny, William meets Rachel Hunter. They find Ian Murray, who was shot with an arrow during the battle and is fevered. Rachel takes Jane and Fanny to a Quaker settlement, while William transports Ian to Jamie. After he resigned his commission, he comes to Lord John's house and offers to search for Benjamin Grey.
In September 1778 William finds the grave that presumably belongs to his cousin Benjamin Grey. However, the body in the grave is not Ben's.
In January 1779 William receives a note from Claire regarding the whereabouts of Amaranthus Cowden.
While searching for Amaranthus, William encounters Fanny and learns that Jane has been arrested for the murder of a British officer and is to be hanged. William tries to speak on her behalf to Lieutenant Colonel Campbell, but fails to save her.
As a last resort, William seeks Jamie's help to rescue Jane. They arrive too late – Jane has killed herself. William gives Fanny into the care of the Frasers.
William and Jamie have a short but honest conversation about William's birth.