Did the CIA help Iran?
This is an incredible story.
The claims about Iran are startling because of the scale of bungling that Mr Risen claims has taken place.
He highlights one operation, known as Merlin, in February 2000, when the CIA allegedly sent a Soviet-era defector to Vienna where, posing an unemployed scientist selling nuclear secrets, he was supposed to contact the Iranians.
The Russian scientist, who had previously worked as an engineer on the Soviet nuclear weapons programme, was given Soviet documents for a key bomb component.
These had been provided by another Russian defector and then doctored by the CIA. Had they used the documents, "instead of a mushroom cloud the Iranian scientists would witness a disappointing fizzle", Mr Risen writes.
But the Russian scientist immediately spotted the flaw and told his CIA handlers: "This isn't right." When told to go ahead with his mission, he apparently feared the Iranians would find the errors and decided to include a letter that alerted them to the flaws in the designs.
Mr Risen describes Operation Merlin as "one of the most reckless operations in the modern history of the CIA, one that may have helped put nuclear weapons in the hands of a charter member of what President George W Bush has called the 'axis of evil' ".
Mr Risen also claims that in 2004 a CIA officer mistakenly sent one of its agents some information that was used by Iran to "roll up" the CIA espionage network in Iran.
"It left the CIA virtually blind in Iran, unable to provide any significant intelligence on one of the critical issues facing the United States - whether Teheran was about to go nuclear," Mr Risen writes.