In July 1776, Grey meets Percy Wainwright – who now uses the name Beauchamp and is a French spy – in Wilmington. Percy wants him to convey a message to the British government that he is willing to provide information on one of Washington's chief officers that could be used to turn that officer, in exchange for the Northwest Territory, which once belonged to France. He also asks him questions about Jamie Fraser, claiming that he is looking for some man and wants to question Fraser, and mentions Grey's step-son William. Grey tells him to stay away from him and his son.
In November 1776, Grey returns to London, where he looks into Beauchamp and finds out that many files pertaining to him have gone missing. However, he learns that a French nobleman is looking for a man named Claudel Fraser, and Beauchamp has been tasked with the search.
Grey also receives a letter from William in which he claims to be in love with Grey's niece Dottie and wants Grey to present his suit for her hand to Dottie's father Hal. Grey doesn't believe William's claims and confronts Dottie in an attempt to figure out what the two are up to, however, he eventually does speak to Hal on William's behalf.
In late December 1776, Grey goes to France to continue his search for information regarding Percy Beauchamp and his connections, which include Denys Randall-Isaacs who currently accompanies William on an intelligencing expedition in Canada. He visits Baron Amandine and meets Dr. Franklin, a prominent Philadelphian. Grey returns to London in March 1777, and he and Dottie leave for Philadelphia in early April, to rescue Dottie's brother Henry who has been seriously wounded and is held prisoner there.
Grey and Dottie arrive in Philadelphia in June 1777. Grey visits the house of Mrs. Mercy Woodcock, a young and married African woman, who nurses Henry. Grey notices that a bond has developed between his nephew and Mrs. Woodcock, and is worried that should she become a widow – her husband is a rebel – Henry might want to marry her, which would cause a family scandal.
On July 4, Grey looks for Dr. Benjamin Rush, who might be able to operate on Henry, whose condition is still serious. Grey finds himself in a taproom where Dr. Rush and other prominent rebels celebrate the first anniversary of the Declaration of Independence. He then notices Percy Beauchamp and the two walk to Southeast Square, where Percy tells Grey the story of Fergus's parents.
The same day, Grey writes letters to his brother Hal, Harry Quarry, a London associate Arthur Norrington who investigates Percy, and to Jamie Fraser. Grey remembers that Claire Fraser experimented with ether, and hopes that she might be inclined to come to Philadelphia to operate on Henry. However, he learns that the Frasers left the Ridge months earlier, intending to visit Scotland.
In September 1777, Grey and Dottie watch British troops commanded by General Howe marching triumphantly into Philadelphia.
In November, William arrives and tells Grey about an excellent Continental surgeon who could help Henry – Denzell Hunter, whom William could fetch from Valley Forge under a flag of truce, along with Hunter's sister and nurse Rachel.
At Christmas, Denzell operates on Henry and becomes engaged to Dottie – they have met in London and fallen in love, and Dottie followed Denny across the ocean.
In April 1778, Claire Fraser comes to Grey's house in Philadelphia, having learned that some months earlier he bought oil of vitriol, which she requires for making ether. They strike a bargain and Claire operates on his nephew Henry.
Grey then learns that the Euterpe has sunk, and as Jamie Fraser is believed to have been on board, Grey delivers Claire news of her husband's death. Grey himself is shattered.
Captain Richardson pays Grey a visit and informs him that he intends to arrest Claire for espionage. Grey proposes to Claire – he can protect her, as well as Fergus's family – and they marry at Grey's house, with William being best man to Grey. Grey and Claire mourn Jamie together and become intimate.
In June, Jamie Fraser, who wasn't aboard the sunken ship, arrives at Lord John Grey's house, followed closely by British soldiers. Grey tries to help him escape, but they are interrupted by William who sees Fraser and realizes the striking resemblance between Jamie and himself. To Grey's horror, Jamie reveals the truth about William's paternity. William is furious with both Fraser and Grey.
As the soldiers come into the house, Jamie pretends to be taking Grey hostage, and William delays the soldiers further, allowing them escape.
Grey and Fraser leave the city, and Jamie thanks Grey for taking care of Claire in his absence. Knowing that Jamie will sooner or later find out that Grey and Claire had sex, Grey admits to him that "he has had carnal knowledge" of Fraser's wife.