Yulia Navalnaya intends to be president of Russia, she tells me. She looks me straight in the eye. No hesitation or wavering.

This, like so many of the decisions she made with her husband, the opposition leader Alexei Navalny, is unambiguous.

Navalnaya knows she faces arrest if she returns home while President Putin is still in power. His administration has accused her of participating in extremism.

This is no empty threat. In Russia, it can lead to death.

Her husband, President Putin’s most vocal critic, was sentenced to 19 years for extremism, charges that were seen as politically motivated. He died in February in a brutal penal colony in the Arctic Circle. US President Joe Biden said there was "no doubt" Putin was to blame. Russia denies killing Navalny.

Yulia Navalnaya, sitting down for our interview in a London legal library, looks and sounds every inch the successor to Navalny, the lawyer turned politician who dreamt of a different Russia.

As she launches Patriot, the memoir her husband was writing before his death, Yulia Navalnaya restated her plans to continue his fight for democracy.

When the time is right, “I will participate in the elections… as a candidate,” she told the BBC.

“My political opponent is Vladimir Putin. And I will do everything to make his regime fall as soon as possible”.

For now, that has to be from outside Russia.

She tells me that while Putin is in charge she cannot go back. But Yulia looks forward to the day she believes will inevitably come, when the Putin era ends and Russia once again opens up.

Just like her husband, she believes there will be the chance to hold free and fair elections. When that happens, she says she will be there.

Her family has already suffered terribly in the struggle against the Russian regime, but she remains composed throughout our interview, steely whenever Putin's name comes up.

Her personal grief is channelled into political messaging, in public anyway. But she tells me, since Alexei's death, she has been thinking even more about the impact the couple's shared political beliefs and decisions have had on their children, Dasha, 23, and Zakhar, 16.

“I understand that they didn’t choose it”.

But she says she never asked Navalny to change course.

He was barred from standing for president by Russia’s Central Election Commission.

His investigations through his Anti-Corruption Foundation were viewed by millions online, including a video posted after his last arrest, claiming that Putin had built a one-billion dollar palace on the Black Sea.

The president denied it.

Yulia says: “When you live inside this life, you understand that he will never give up and that is for what you love him”.

Navalny was poisoned with the nerve agent Novichok in 2020.

He was flown to Germany for treatment and the German chancellor demanded answers from Putin’s regime.

Navalny worked with open-source investigators Bellingcat and traced the poisoning to Russia’s security service, the FSB.

He began writing his memoir as he recovered.

He and Yulia returned to Russia in January 2021 where he was arrested after landing.

Many ask why they returned.

“There couldn’t be any discussion. You just need to support him. I knew that he wants to come back to Russia. I knew that he wants to be with his supporters, he wanted to be an example to all these people with his courage and his bravery to show people that there is no need to be afraid of this dictator.

“I never let my brain think that he might be killed… we lived this life for decades and it’s about you share these difficulties, you share these views. You support him”.

After his jailing, Navalny continued his book in notebook entries, posts on social media and prison diaries, published for the first time. Some of his writing was confiscated by the prison authorities, he said.

Patriot is revealing - and devastating. We all know Navalny’s final chapter, which makes the descriptions of his treatment - and his courage in the face of it - even more poignant.

Navalny spent 295 days in solitary confinement, punished, according to the book, for violations including the top button of his fatigues being unbuttoned. He was deprived of phone calls and visits.

Yulia Navalnaya told me: “Usually, the normal practice is banishment just for two weeks and it's the most severe punishment. My husband spent there almost one year."

In a prison diary from August 2022, Navalny writes from solitary confinement:

It is so hot in my cell you can hardly breathe. You feel like a fish tossed onto the shore, yearning for fresh air. Most often, though, it is like a cold, dank cellar….. It is invariably isolated, with loud music constantly playing. In theory, this is to prevent prisoners in different cells from being able to shout to each other; in practice, it is to drown out the screams of those being tortured.

Navalnaya says she was prevented from visiting or speaking to her husband for two years before he died. She says Alexei was tortured, starved and kept in "awful conditions".

After his death, the US, EU and UK announced new sanctions against Russia. These included freezing the assets of six prison bosses who ran the Arctic Circle penal colony and other sanctions on judges involved in criminal proceedings against Navalny.

Yulia calls the reaction to his death by the international community “a joke” and urges them to be “a little less afraid” of Putin. She wants to see the president locked up.

“I don’t want him to be in prison, somewhere abroad, in a nice prison with a computer, nice food… I want him to be in a Russian prison. And it’s not just that - I want him to be in the same conditions like Alexei was. But it’s very important for me”.

The Russians claim Navalny died of natural causes. Yulia believes President Putin ordered the killing.

“Vladimir Putin is answering for the death and for the murder of my husband”.

She says the Anti-Corruption Foundation she now leads in her husband’s place already has “evidence” which she will reveal when they have “the whole picture”.

The book is as much a political work as a memoir, a rallying cry to anyone who believes in a free Russia. It is also being published in Russian, as an ebook and audiobook. But the publishers won’t send hard copies to Russia or Belarus, because they say they can’t guarantee the book would get through customs.

How many Russians will dare to buy it, even in electronic form, is unclear - and how much impact it could have remains questionable.

The message etched on every page is that Navalny never gave up. His arch wit shines through.

He says, in the punishment cell, he is getting “for free” the experience of staying silent, eating scant food and getting away from the outside world that “rich people suffering from a midlife crisis” pay for.

Only once does he share feeling “crushed”, during the hunger strike he undertook in 2021 in order to demand medical care from civilian doctors. “For the first time, I’m feeling emotionally and morally down,” he writes in one entry.

But Yulia says she never worried that he would actually be broken by the regime.

“I'm absolutely confident that is the point why finally they decided to kill him. Because they just realised that he will never give up”.

Even the day before he died, when he appeared in court, Navalny was filmed joking with the judge.

Yulia says laughter was his “superpower”.

“He really, truly laughed at this regime and at Vladimir Putin. That's why Vladimir Putin hated him so much”.

The writing is laced with a great deal of irony.

The book will sell better if he dies, Navalny writes:

Let’s face it, if a murky assassination attempt using a chemical weapon, followed by a tragic demise in prison, can’t move a book, it is hard to imagine what would. The book's author has been murdered by a villainous president; what more could the marketing department ask for?

In the end, Patriot is also a love story about two people fully committed to a cause they believed in.

A cause for which Yulia has now become the figurehead.

After a visit from her, Navalny writes:

I whispered in her ear ‘Listen, I don’t want to sound dramatic, but I think there’s a high probability I’ll never get out of here…. They will poison me’.

‘I know’, she said with a nod, in a voice that was calm and firm. ‘I was thinking that myself’...

It was one of those moments when you realise you found the right person. Or perhaps she found you.

‘Yulia Navalnaya: The Interview’ is on BBC Two at 1900 on Monday 21 October and on the iPlayer

Patriot is published on Tuesday 22 October