The novel tells the intersecting stories of various people, with the major themes involving Germany during the Cold War, the age of Wikileaks and other exposers of government secrets, and one woman's gradual realization of who her biological father is.

The two have a unique and co-dependent relationship, with her mother refusing to tell Pip anything about her father or even her previous life, including Penelope's real name and age.

Pip works as a telemarketer for a company selling dubious green-energy schemes; she lives in a communal, squat rent-free house because of her secret love for a married man named Stephen.

After impressing one of the visitors to the squat, a beautiful German anti-nuclear activist, Annagret, she is recruited for The Sunshine Project, a fictional competitor to WikiLeaks, headquartered in Bolivia and run by a man named Andreas Wolf.

In 1987, Andreas Wolf is 27 and living in East Germany, where he acts as a youth councillor for a church, routinely having sex with the teenaged girls he councils.

As her mother is a nurse who's addicted to drugs and has been stealing them and her stepfather, Horst, is a low-level Stasi informant, Annagret does not feel that she can report the abuse because one or both of her parents will be imprisoned, thus ruining her life.

Born to an English literature professor and a high-level official in the East German government, he is indulged as a child due to his parents' status, his intelligence, and his good looks.

When a poem of his is published which contains an obscene and treasonous acrostic, he is protected by his parents, but warned that he must either complete the army service he has been avoiding or become estranged from them.

Two years later, as the Berlin Wall is about to come down and Wolf is afraid that his crime will be exposed when the Stasi files are unsealed, Andreas approaches his father and arranges for one last favor from the party.

While trying to leave the building with those records, he is almost caught before he runs into television cameras and denounces the government, thereby quickly becoming a celebrity dissident, shining "sunlight" on the state's secrets.

Pip goes to work in Bolivia, which she loves, but is dismayed by the bizarre hierarchy at The Sunshine Project where status is determined by proximity to Andreas Wolf.

Their marriage quickly becomes abusive, as Anabel descends into anorexia and isolates Tom from members of his family and his own friends, and does her best to punish him for his journalistic success.

He becomes an internet celebrity and a wanted man in most countries of the world for his leaking of secrets, and eventually bases his operations in a hidden paradise within Bolivia.

In his growing paranoia, he endlessly searches for information about himself, and when a journalist, Leila Helou, castigates him for "dirty secrets," he connects her with Tom Aberant, who he is convinced has betrayed him.

Seeking revenge, he discovers that Tom's wife vanished long ago, so he starts a deep trawl with face-recognition software on American databases.

Pip convinces her mother to dip into the huge fund to pay off some important bills, and arranges for Tom to meet Anabel again after 25 years.

[4] Jonathan Galassi, president and publisher of Farrar, Straus and Giroux, described Purity as a multigenerational American epic that spans decades and continents.

[16] The novelist told Toronto Star, "So, people with a lot of time on their hands and no real interest in what is true think I’m a bad person — So what?

It’s not going to end my career.”[17] Michiko Kakutani's review in The New York Times was favorable,[18] calling the book "dynamic" and dubbing it Franzen's "most intimate novel yet."

Harper's described the novel's plot as a "beautiful arabesque," and suggests that Franzen seems to have responded to past accusations of anti-feminist chauvinism with blunt clichés.

[21] In 2016, Daily Variety reported that the novel was in the process of being adapted into a 20-hour limited series for Showtime by Todd Field who would share writing duties with Franzen and the playwright Sir David Hare.

[24] In 2017, The Hollywood Reporter quoted Showtime CEO David Nevins as saying that after Craig's commitment to the 25th James Bond movie, the Purity adaptation was still on track.