It's the kind of drama politics offers but rarely delivers.  But on Tuesday, Senator Mike Duffy provided both the drama and a plot twist in the Senate expenses scandal worthy of the best whodunits.

In the space of just a few minutes, Duffy portrayed Prime Minister Stephen Harper as the catalyst in what he called a conspiracy to force him to repay $90,000 in living expenses.

Drawing on his years of experience as a broadcaster, the senator once again became a storyteller, weaving a tale of intrigue, intimidation and betrayal.

What happens today

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He told the assembled senators — who were there to debate a motion to expel him and two other senators, Pamela Wallin and Patrick Brazeau, from the upper chamber — that he was attending against the orders of his doctors who feared the exertion would worsen his existing heart condition.

He came, he said, to defend his good name.

In the process, he accused other, leading Conservatives of bribery and extortion in forcing him to repay the housing expense money that auditors had viewed as improper. And he told the senators that he can back up his claims with all kinds of emails, which are now in the hands of his lawyer and the RCMP.

In the process, the senator from Prince Edward Island has put his credibility on the line against that of the prime minister.

Duffy said he met with Harper, and the PM's former chief of staff, Nigel Wright, on February 13 to discuss his expenses. But Harper wasn't interested in his explanations or the truth.

"It's not about what you did,'' he quoted Harper as saying. "It's about the perception of what you did that's been created in the media. The rules are inexplicable to our base.''

Harper ordered him, Duffy said, ''Pay the money back. End of discussion. Nigel Wright was present throughout. Just the three of us.''

The three-month gap

But he didn't stop there. Duffy called his former tormentors out by name, several of them, who sat across from him in the Senate as he spoke.

He accused them of pressuring him to repay the money against his will, and threatening to have him kicked out of the Senate unless he resigned from the Conservative caucus.

The prime minister's spokesman, Jason MacDonald, dismissed Duffy's portrayal of the meeting as nothing new.

"It's on the public record,'' he said in a statement. "The prime minister made it clear any inappropriate expenses should be repaid. That's it. That's the only time the prime minister discussed Mr. Duffy's expenses with him.''

According to the prime minister himself, it's also the last time he ever talked to anyone about the matter until May 15, when he learned from media reports that Wright had concluded a secret deal with Duffy to repay the $90,000 in expenses.

That's three months without showing any interest in whether Duffy had followed his orders, or inquired about what had been done to close the matter.

Accountability, retribution

Harper held fast to that line again on Tuesday in another question period dominated by the Senate scandal, but before Duffy's bombshell landed.

"Does the prime minister regret any of his own actions in the Senate scandal,'' NDP Leader Thomas Mulcair started off.

"Once again, as I've said before,'' Harper replied, ''We expect that when people are parliamentarians in either house that they respect rules… and if they don't, we expect there to be accountability.''

Liberal Leader Justin Trudeau tried, too, to get the prime minister to respond, narrowing his focus to the secret deal between Wright and Duffy.

"Will the prime minister take any personal responsibility for this abuse of Canadians trust?''

Harper insisted once again that he has repeatedly stated his opposition to, and non-involvement in, the deal by his former right-hand man, Nigel Wright.

Brazeau-Wallin-Duffy

Three Conservative senators, appointed by Stephen Harper in 2008, now face expulsion without pay. From left, Patrick Brazeau, Pamela Wallin, Mike Duffy. (Canadian Press)

"We don't assure Canadians that everything will be perfect. But we do assure Canadians that when anything goes wrong people will be held accountable,'' he said.

"The misuse of expense accounts is not appropriate and will be dealt with appropriately.''

Accountability. Retribution. Those are the themes Harper prefers.

He returned to them throughout question period, and for good reason. His message wasn't just for MPs, but for Conservative supporters out there who remember that accountability and Senate reform were issues that propelled the party to power in 2006 on the heels of the Liberal sponsorship scandal.

Seven years on, many of those same folks appear to be wondering where the commitments went.

They are also the audience Harper's playing to with his gambit of suspending Duffy and the other two senators before any charges might even be laid, and over the objections of other senators, including some Conservatives.

Opponents of the move are now arguing that suspending the three infringes their right to due process, not to mention the Senate's own long-standing practice of waiting for any criminal charges to be concluded before taking punitive action against a member.

Many Conservatives, however, appear willing to accept that trade-off, their demands for accountability trumping the rights of colleagues.

"It doesn't hurt this government to have senators squabbling with senators about the rights of senators,'' said one Conservative strategist.

But Duffy's effort to recast himself from villain to victim is having an impact.

First, it guarantees the prime minister will be back on his feet again Wednesday, presumably to deny he knew anything about the deal, and to sidestep questions about why he insisted in May that Wright acted alone.

Second, it creates a credibility contest between Harper and Duffy. For the first time, the senator's version of the story is being given a full public airing, and, for the time being at least, he's casting doubts about the government's version of events.

Canadians already knew from RCMP documents that Nigel Wright did not act alone as the prime minister first suggested. At least three other former members of his office were aware of the repayment scheme.

The government's own talking lines — that Wright acted alone — morphed long ago into claims that Harper's former chief of staff accepted sole responsibility.

These are the kinds of shifts in messaging the opposition continues to highlight when challenging the credibility of the government's claims.

Duffy's first public comments on the scandal has given them new ammunition, even if the Conservative-dominated Senate endorses the government's efforts to suspend him and the others without pay.

It's now Duffy's word against the prime minister's. A battle for credibility that only one of them can win.