For years, Marina Litvinenko’s life with her husband seemed to be set apart from the world he inhabited. In Russia, when they met in 1993, she was a professional ballroom dancer. He was an officer of the post-Soviet F.S.B. domestic security agency.

After their flight to London in 2000, she once told me, she settled happily into the world of a homemaker in the uneventful district of Muswell Hill in north London, raising their son Anatoly. On the evening of his fateful encounter at the Millennium Hotel in Grosvenor Square, she had prepared his favorite chicken dish to celebrate the sixth anniversary of their arrival in London.

By contrast, her husband spent his days seeking a niche in the half-light between government intelligence agencies and private security companies trawling for information. According to his widow, he was a paid agent of the British Secret Intelligence Service, and had ties to Spanish intelligence.

But his death upended everything, casting her into the public eye as the champion of a cause. “It is not just in my interest to get to the truth of this,” she said recently. “It is in the public interest. It’s for everyone in Britain to ask: why? Who did it?”

At every turn, though, her efforts to secure a full inquiry have been thwarted. The latest obstacle came last week when three high court judges turned down a request to set a formal limit on the potentially ruinous costs she might incur from the fees charged by government lawyers if she loses the next battle in her continuing fight for a full inquiry. Her own legal team is acting pro bono.

“What I am doing, I am doing for my husband,” she told The Guardian. “But if I decide to carry on, there is a huge risk that we will be homeless and will lose everything. I need to take some very serious decisions.”

Days later, a lawyer acting for her said, she resolved to “continue her fight to uncover the truth about her husband’s death, despite mounting adversity.”