ghostwriter (Ewan McGregor) is hired by publishing firm Rhinehart, Inc. to complete the autobiography of former British Prime Minister Adam Lang (Pierce Brosnan). The writer’s predecessor and Lang’s aide, Mike McAra, has recently died in an apparent drowning accident. The writer travels to Old Haven on Martha’s VineyardMassachusetts, where Lang and his wife Ruth (Olivia Williams) are staying in a harshly modernistic mansion, along with Lang’s personal assistant (and implied mistress), Amelia Bly (Kim Cattrall), and staff. Amelia forbids the writer from taking McAra’s manuscript outside, emphasising that it is a security risk.

Shortly after the writer’s arrival, former Foreign Secretary Richard Rycart (Robert Pugh) accuses Lang of authorising the illegal seizure of suspected terrorists and handing them over to be tortured by the CIA, a possible war crime. Lang faces prosecution by the International Criminal Court unless he stays in the United States (or one of the few other countries that do not recognise the court’s jurisdiction). While Lang is in Washington, D.C., the writer finds items in McAra’s room suggesting he might have stumbled across a dark secret. Among them is an envelope containing photographs and a phone number the writer discovers is Rycart’s.

During a bike ride, the writer encounters an old man (Eli Wallach) who tells him the current couldn’t have taken McAra’s body from the ferry where he disappeared to the beach where it was discovered. He also reveals a neighbour saw flashlights on the beach the night McAra died, but she later fell down the stairs and lapsed into a coma.

Later, Ruth admits to the writer that Lang had never been very political and until recently always took her advice. When the writer tells her the old man’s story, she suddenly rushes out into the rainy night to “clear her head”. Upon returning, she reveals Lang and McAra had argued the night before the latter’s death. The writer and Ruth have a one night stand while Adam is away.

The next morning, the writer takes the BMW X5[5] McAra used on his last journey. Unable to cancel the pre-programmed directions on the car’s sat-nav, he decides to follow them. He arrives in Belmont, Massachusetts at the home of Professor Paul Emmett (Tom Wilkinson).

Emmett denies anything more than a cursory acquaintance with Lang, despite the writer’s showing him two pictures of the pair among photographs found in McAra’s possessions, as well as pointing out a more recent one on the wall of Emmett’s study. When the writer tells Emmett the sat-nav proves McAra visited him the night he died, Emmett denies meeting McAra and becomes evasive.

The writer leaves and successfully eludes a car that is pursuing him. He boards the ferry back to Martha’s Vineyard, but when he sees the pursuit car drive aboard, he flees the boat at the last moment and checks into a small motel by the ferry dock.

With no one else to turn to, the writer redials Rycart’s number and asks for help. While waiting, the writer researches Emmett, and finds links between Emmett’s think tank and a military contractor. He also finds leads connecting Emmett to the CIA. When Rycart arrives, Rycart reveals McAra gave him documents linking Lang to so-called “torture flights”, in which terrorist suspects were placed on private jets owned by Emmett’s company to be tortured while airborne.

Rycart further claims that McAra found new evidence, which he wrote about in the “beginnings” of the manuscript. The men cannot, however, find anything in the early pages. The writer discusses Emmett’s relationship with Lang, while Rycart recounts how Lang’s decisions as Prime Minister uniformly benefited US interests.

When the writer is summoned to accompany Lang on his return flight by private jet, he confronts Lang and accuses him of being a CIA agent recruited by Emmett. Lang derides his suggestions.

Upon leaving the aircraft, Lang is assassinated by a British retired soldier whose son died “in one of Lang’s illegal wars”. The assassin is in turn shot dead by Lang’s bodyguards. Nevertheless, the writer is asked to complete the book for posthumous publication, as in light of Lang’s death it will be a certain best-seller.

Amelia invites the writer to the book’s launch party in London, where she unwittingly tells him the Americans tightened access to the book, as the “beginnings” contained evidence threatening national security. She also tells him Emmett, who is in attendance, was Ruth’s tutor when she was a Fulbright scholar at Harvard.

The writer realizes the clues were hidden in the original manuscript, in the opening words of each chapter, and discovers the message: “Lang’s wife Ruth was recruited as a CIA agent by Professor Paul Emmett of Harvard University.” He concludes Ruth shaped Lang’s every political decision to benefit the United States under direction from the CIA.

The writer passes a note to Ruth revealing his discovery. She unfolds the note and is devastated. She sees the writer raising a glass to her but is kept from following him by Emmett and other assistants.

The writer leaves the party and attempts to hail a taxi, without success. As he crosses the street off-camera, a car accelerates in his direction, and a thud is heard. Witnesses react in horror, and the pages containing McAra’s manuscript scatter in the wind. The film ends, leaving the writer’s fate unconfirmed.