New Zealand politics, concedes Bryce Edwards, one of the country's leading commentators on the subject, "can tend to be on the bland side compared with other countries."

And at the start of last month, New Zealand's impending September 20 general election looked set to be just that: a tame affair, with an all but foregone conclusion.

The center-right National government, led by perennially popular Prime Minister John Key, enjoyed a huge lead in the polls and seemed destined to amble its way to a third term in power.

But then a bombshell struck in the form of a book-length piece of investigative journalism, triggering a cascade of scandals that have thrown the political parties' campaigns into disarray and dominated the news cycle for weeks.

"No campaign in living memory compares to the 2014 campaign," said Edwards, a lecturer in politics at the University of Otago.

"New Zealand election campaigns are usually fought over a mixture of policy and personalities," he told CNN, "not over issues of integrity and corruption and wrongdoing."

Last month, long-time freelance investigative journalist Nicky Hager published "Dirty Politics." The book is based on a cache of emails and social media messages hacked from the private accounts of the controversial right-wing blogger Cameron Slater, whose "Whale Oil" blog is widely read.

Slater, a polarizing and politically well-connected figure whose father is a former National Party president, is notorious for his abrasive style and for breaking a string of scandals, including an extramarital affair by the mayor of Auckland last year. The mayor subsequently acknowledged the affair.

Hager's book alleges close and sustained cooperation between the blogger and senior government figures -- including a senior minister and top prime ministerial aides -- in their concerted efforts to smear political adversaries.

The extent of the alleged collaboration suggested in the hacked emails surprised even the book's author, he told CNN.

"This was prime ministerial staff involved in coordinating and executing attacks on the government's political opponents," said Hager. "It was much more orchestrated and constant -- relentless -- than anyone had been aware."

(CNN)