Nazi "assassins", mischievous con-artists and power hungry spies... Black Sheep investigates how a pair of hoaxers convinced the government that New Zealand had been infiltrated by Nazi agents.

In 1942 the head of New Zealand's first spy agency, the Security Intelligence Bureau (SIB), sent a shocking letter to the Prime Minister.

Major Kenneth Folkes told Peter Fraser that Nazi agents had infiltrated New Zealand. He said the Germans had established a network of saboteurs and were planning on blowing up critical infrastructure and assassinating top level politicians.

But... the Nazi conspiracy was a hoax, and some historians think Major Folkes deliberately expanded that hoax in an effort to get more power for the SIB.

The hoax was dreamed up by two criminals Alfred Remmers and Sydney Ross, who were serving time together in Waikeria prison.

"Remmers was a policeman," says Sherwood Young, a retired police historian. "He was dismissed because he committed a crime - burgling houses while he was on the beat."

Young says Remmers was the mastermind of the hoax but needed a partner in crime to pull it off. " was a man who is sadly dying. Within a very short time he's dead of leukemia and he's in need of some conman to do the legwork."

That conman was Sydney Ross, a fraudster and safebreaker.

"He saw himself as a clever guy who could get away with things," says Beverly Price, who helped her late husband Hugh Price write a book on the Syd Ross hoax, The Plot to Subvert Wartime New Zealand.

After being released from prison in March 1942, Ross rang the Minister for Public Works and told him he'd been approached by Nazi conspirators who wanted to use his experience in safebreaking to blow up critical infrastructure to weaken New Zealand ahead of a German invasion.

"Ross started off with utter honesty," says Beverly Price. "His way of handling his hoax all along was a mixture of what was true and verifiable; and the fantasy - that there were conspirators trying to get in touch with him."

The government might have dismissed his story if not for a remarkable coincidence. The Prime Minister had just been told that a plot very similar to the fake conspiracy Ross was describing had just been uncovered in Australia.

Just days after Ross came forward, the headline of the Evening Post looked like this:

It turned out a proto-fascist group called "Australia First" (no relation to the current Australia First political party) were planning on blowing up infrastructure and distributing propaganda to smooth the way for a Japanese invasion…

Go to this episode on rnz.co.nz for more details