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Shane Bauer, the American hiker who, along with friends Sarah Shourd and Josh Fattal, were taken prisoner by Iranian authorities in 2009, speaks about his experience and about the memoir they wrote together, at the Oakland, Calif. apartment he shares with Shourd, Tuesday, March 4, 2014. The book will be published on March 18. (D. Ross Cameron/Bay Area News Group)

OAKLAND -- Stuck for 26 months in a grim Iranian prison, Shane Bauer often let his mind drift to the shores of Lake Merritt.

He would daydream of jogging around Oakland's bustling urban lake on a sunny day. And when he and cellmate Josh Fattal surprised Sarah Shourd, Bauer's fiancee, with a makeshift birthday celebration in the Tehran prison's courtyard, they all imagined picnicking together on a lakeside lawn.

Now the three UC Berkeley graduates who in 2009 inadvertently hiked from Iraq into the hands of the Iranian military have written an intimate memoir about their captivity and campaign for freedom. The friends grew together, apart and together again as Iran accused them of being U.S. spies and their lives became entangled in a geopolitical pawn game.

"The three of us were so connected that it was impossible for one of us to have a really hard time without all of us having a really hard time," said Shourd, interviewed with Bauer at their new apartment just a few blocks east of Lake Merritt. They titled the book "A Sliver of Light," after the sunlight that helped sustain them when it shone into their cells each morning through a barred window -- and after the hope for freedom they always had but many prisoners don't.

With sunlight, "we could track time," said Shourd, who was released a year earlier than Bauer and Fattal but spent the entire time in solitary confinement. "The way it would come through the window and move across the wall became monumental for us."

Shourd and Bauer are now married; Bauer proposed in prison with a ring of thread. Both are using their ordeal to expose what they think are similarly unjust prison practices in California, where many inmates are held in isolated "Security Housing Units." Though not always solitary -- many SHU inmates share a cell -- the extreme confinement has a similar psychological effect, the couple said. Many of the California units are windowless, and the prisoners' only outdoor time happens in a high-walled concrete pen.

"Getting through a year (of isolation) was the hardest thing I've ever had to do," Shourd said. "I've heard of people who have been in for 10, 20 years."

Shourd is now a writer and advocate for nonprofit group Solitary Watch who is collecting the stories of isolated inmates around the country. Bauer is an investigative journalist who works in the San Francisco office of Mother Jones, the same magazine he sent dispatches from the Middle East before his incarceration. Fattal now lives in New York but is reuniting with his friends for a cross-country book tour that comes to Berkeley, Los Altos and San Francisco later this month. The book was scheduled for Tuesday release.

The 352-page account reveals many details of their detention not previously disclosed, including how they struggled to keep their relationships with one another from fraying under harsh conditions. Among the surprises is how often they defied the authority of the guards and interrogators who professed collegiality but held power through manipulation, expecting appreciation for small concessions.

The prison allowed the Americans to read books sent by their families, but it refused them pens or paper to write.

Still, in one of many acts of defiance, when Iran allowed the trio's parents to visit them, Bauer slipped a detailed note to his mom that had been folded between two of his fingers. She, in turn, slipped it into her bra.

Bauer hopes his captors read the book. During their last year of detention after Shourd was released on "humanitarian" grounds, Bauer said that he and Fattal sought to interrogate their interrogators by trying to "make them recognize the position they were in."

"I realized kind of the mentality they had where they thought they weren't doing anything wrong," he said. "I hope that something gets inside of them that helps them see what they're doing, how they hurt people."

The friends were housed in the same political wing of Tehran's Evin Prison as Iranian dissidents and members of al-Qaida. They sometimes heard the cries of inmates beaten by guards.

The book recounts the oft-told story, still disputed, of how the friends ended up captured near the Iran-Iraq border after hiking through a popular local tourist region of Iraqi Kurdistan. What it does not have is any conclusion on why Fattal and Bauer were finally released by Iran in September 2011.

"To this day, I don't know what did it," Shourd said. "I believe the pressure internationally built to the point where Iran (was getting) diminishing returns on their investment."

"Sliver of Light" readings
What: Shane Bauer, Sarah Shourd, Josh Fattal tell their story of imprisonment in Iran for more than two years in their book "A Sliver of Light."
March 27, 7:30 p.m., Berkeley Arts and Lectures
March 28, 7 p.m. Commonwealth Club, Los Altos
March 31, 7 p.m. Jewish Community Center of San Francisco