Leona Alleslev says her decision to cross the floor to the Conservative Party in dramatic fashion on the first day of the fall sitting wasn't one she made lightly — or in a hurry.

"I didn't make that final decision until I stood up in the House," she said Monday in an interview on CBC News' Power & Politics.

There was evidence of nervous anticipation in the Commons in the minutes prior to her announcement, which happened right in the House of Commons just before question period Monday. Fewer than 20 Liberal MPs were seated around her at the time — but the Conservative benches were full.

Keeping her cards face down

Alleslev sat with her hands clasped as she waited for the Speaker to call on her to rise during a debate on the Comprehensive and Progressive Agreement for Trans-Pacific Partnership, Ottawa's new Asia-Pacific trade pact. She made small talk with John Aldag, the Liberal MP who sat next to her. She quickly checked her phone — then placed it face down on her desk, so that the screen was concealed.

In front of her was an off-white file folder holding the speech that would cement her departure from the Liberal caucus. When the Speaker indicated that her moment was coming soon, she took out her notes and placed them face down on her desk. (Normally, MPs read over their statements as last-minute preparation before they rise in the Commons.)

It was clear Alleslev didn't want anyone to see what she was going to say. Just one last secret to keep at the end of a secret process that started at a Sheraton hotel near Toronto's Pearson Airport in early August.

That's when Alleslev met Conservative Party Leader Andrew Scheer. The meeting happened at her request. ​Alleslev told colleagues on both sides of the aisle that it was the culmination of months of swelling frustration.

As a former business owner, she was particularly vocal about the small business tax changes her then-party introduced last year. Her Air Force background fed her frustrations about the used fighter jets the Liberals' announced they would buy last June.

Her former comrade in uniform, Conservative MP Erin O'Toole, told her (half joking) that she was in the wrong party. Conservative MPs James Bezan and Rob Nicholson told her the same thing. Though she laughed it off at first, the idea started to grow on her — and more formal talks with those Conservative MPs began.

In late July, still a member in good standing of Team Trudeau, Alleslev tweeted a welcome to the prime minister when he came to visit her riding at the end of July. The following month, Alleslev requested a sit-down with Scheer.

'Really hitting it off'

The meeting happened in a private meeting room at the airport Sheraton. It was scheduled to last an hour; it lasted two and a half hours. It was the only meeting that took place in person between the two politicians. Alleslev described herself and Scheer as "really hitting it off."

She said she sought assurances that she would be able to speak her mind in the Conservative caucus without retribution. She said she received them.

The plan to roll the floor crossing out was crafted over the last few weeks — an effort led in part by Conservative campaign manager Hamish Marshall

Even the Aurora-Oak Ridges-Richmond Hill federal Liberal Association was caught off guard.

"I had no prior knowledge of this event, and it was done without my consultation. It is one that I struggle to understand," wrote president Clayton Haluza in a statement Monday.

Party operatives helped Alleslev craft her speech and talking points for the big day; they describe her mood at the time as determined but nervous.

As the 1:30 p.m. statement in the House approached, Alleslev even hugged some of her Liberal colleagues — minutes before she stunned them all by walking away.

With files from David Cochrane