"The Ghost" (Ewan McGregor) is brought on board to finish the memoirs for former British Prime Minister Adam Lang (Pierce Brosnan) after the apparent suicide of his predecessor. During this time, Lang is under investigation for handing over terrorist suspects to the CIA for torture.
The Ghost finds out that his predecessor was murdered after finding out that, Lang's colleague at Cambridge, Paul Emmett (Tom Wilkinson) was a CIA agent and that it was Lang's CIA connection that got him elected. It was also revealed that the war crimes investigation was started after The Ghost's predecessor gave the information he found out to Lang's former Foreign Secretary Richard Rycart. However, soon after The Ghost confronts Lang with this information, which results in him angerly confessing to the war crimes, Lang is assassinated by a protester that kept showing up in the film.
The Ghost is encouraged by his agent to finish Lang's memoirs and is invited by Lang's assistant Amelia Bly (Kim Cattrall) to the book opening. He is shocked to find out that Emmett is in attendance, the reason being that he was a former college advisor to Lang's wife Ruth (Olivia Williams). This results in The Ghost remembering a comment Rycart made about how his predecessor hid the secret to Lang's CIA connection at the beginning of the memoir's manuscript. The Ghost takes the manuscript and, after examining the pages, finds out that the first word of each chapter spells a phrase revealing that Ruth was in fact a CIA agent, recruited by Emmett.
The Ghost passes this phrase to Ruth, signalling that he found out the truth. However, as he is leaving with the manuscript, a black car comes speeding after him and it is assumed that The Ghost is run over off screen.
The film ends with the pages of the manuscript blowing down the street.