NICOLA Sturgeon is in a passionate mood.

Even sitting at a table in her fourth-floor Holyrood office, there's a touch of the boxer's bob and weave about the Deputy First Minister, a restless energy as she discusses what 2014, the year of the independence referendum, means to her.

"It's going to be the most exciting phase of my political life," she says of the coming months. "It's something I passionately believe in; I've passionately believed in it throughout all of the years I've been in politics.

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"It has always seemed to me to be the means to the end of all I want to do in Scotland, which is play a part in making it the kind of country I believe we can be. I don't find it hard to motivate myself for this."

Despite the poor poll ratings - Sturgeon readily admits the Yes side is trailing - she seems on good form, buoyed by finally delivering the SNP's White Paper on the mechanics of independence, and convinced that the Yes side's positivity will prove contagious before September arrives.

After October's reshuffle deprived Michael Moore of the job, she also seems pleased to have a new Scottish Secretary as a scratching post. In her first TV debate with him, she left the Liberal Democrat MP Alistair Carmichael in ribbons.

"I don't feel sorry for him," she says, rather taken aback at the suggestion she might. "I still struggle to understand the decision to replace Michael with Alistair. Alistair may, over the course of the next few months, explain that decision in how he performs, but right now I struggle to get the rationale for it."

It's not all Tiggerish bounce, of course. The referendum is daunting as well as inspiring, especially when the hopes of so many friends and colleagues are projected on to you.

"I don't think you'd be human in the job that I'm doing now if there wasn't a degree of apprehension and nerves about it," she says. "Is it daunting in terms of the sheer weight of responsibility? Of course it is. It's challenging, but I think the overwhelming emotion I feel is anticipation and excitement and a real keenness to get on with it. I think the possibilities for Scotland if we vote Yes are so immense that I just want to throw everything at it over the next few months and try to enjoy it along the way."

If her husband - Peter Murrell, the SNP's chief executive - can persuade her, she might "take a few days off at the start of the summer", though she will not truly relax all year.

But while excitement and passion are necessary for a Yes vote, they are not sufficient. A lot of old-fashioned, unglamorous graft must be done if the Yes side is to win, with mass door-knocks, canvassing trawls and voter registration drives all imminent.

Sturgeon says early 2014 will bring three key strands to the fore from the Yes side: a focus on the economic upsides of independence, a push on bread-and-butter issues such as pensions rather than minority interest arcana such as EU entry negotiations, and putting the No campaign on the spot about what would befall Scotland if it stays in the Union.

She gives an example of the latter approach: "Tell us what life will look like in Scotland if we vote No. You've demanded answers from the Yes campaign, you've got those answers, give us some answers of your own."

The focus will be "pretty ruthless", she says. "I think we will see momentum start to build for the Yes side because the No side have got nothing to offer than the increasingly tired scaremongering campaign that they've pursued throughout the year. I think they're starting to exhaust the patience of the public. All relentlessly and exclusively negative campaigns fall into this trap eventually.

"If you say 'Boo' once, you frighten somebody. You say it again, you don't frighten them quite as much. In order to try and keep getting an impact, you've got to be more and more outlandish. The point at which they tell folk they cannae watch Doctor Who is the point at which they undermine the credibility of pretty much everything they say."

But isn't there an equivalent risk to the Yes side? That after a while all that evangelical optimism becomes a liability, that you start to sound unworldly and simple-minded? As if on cue, her serious face arrives. "I never have been the kind of Nationalist who says the streets are paved with gold. Scotland, like every other country on the planet, will have its challenges.

"It will have its ups and downs. Fiscally, financially, economically, we've got a lot going for us. But whether we, in the future, are a successful country or not would come down to the quality and good sense of the decisions we make.

"We face challenges - demography [a growing elderly population], constrained public finances - but the question is: does independence better equip us to face these challenges or not, and I think it does. I don't take a view that just by the snap of your fingers or waving a wand, becoming independent makes everything fine. But it does put you in charge of your own destiny, and that's always a better place to be."

After months of mindless, one-dimensional cheerleading from Yes Scotland, it's a relief to hear a more realistic note in the debate. The 43-year-old Glasgow Southside MSP even deals with politics' ultimate taboo: defeat.

Whenever her boss, Alex Salmond, is asked about losing, he falls back on a moth-eaten quip about only contemplating scenarios predicated on success, but Sturgeon addresses the personal impact of a No vote in September head-on.

"I'd be gutted," she admits. "I'll be gutted. But will I stop believing in independence, will I stop arguing for independence? The SNP will still be in Government. We'll still have a country to govern. We'll fight the election in 2016.

"But I genuinely don't spend a lot of time thinking how I'll feel if there's a No vote. If that happens I'll cross that bridge and I'll deal with that at the time. But I'm sure you will understand that with nine, 10 months to go, I try and use all my mental energy to bring about the alternative."

But is nine months enough? "It's what we've got, so it has to be enough."

There is a lot in Yes's favour, she insists. Besides "the right message and the right team", she detects a "real jitteriness and nervousness" in the No camp, the result, she reckons, of growing tensions between Labour and the Tories, and internal polling.

The latter, she says, will have picked up on the same trends as the Yes camp's polling - fewer determined No voters, more undecideds, and the Yes message resonating with traditional non-voters, of whom there are two million in Scotland.

"Generally speaking, people who don't vote don't like the status quo. Therefore, there is a natural inclination for people in that category to support the Yes campaign," she says.

If the Yes side can tap into that huge reservoir of potential votes, it really would be game on. The excitement hasn't peaked yet.