BEIJING — The 20 or so activists gathered at an isolated guesthouse on the outskirts of the capital, leaving their cellphones behind to avoid detection by the police. China’s first leadership change in a decade was fast approaching, and the group saw an opening for a movement to fight injustice and official corruption.

That day, in May 2012, they began work on a plan to expand the New Citizens Movement, an ambitious campaign for transparency and fairness that would eventually draw as many as 5,000 supporters, inspire street protests across the country and provide the first major test to help gauge the new leadership’s tolerance for grass-roots political activism.

They were heartened when China’s new leader, Xi Jinping, came to power that November, vowing to stamp out corruption, promote judicial fairness and respect the Constitution, goals tantalizingly close to their own.

Now, 14 months later, their ideals have collided with a harsh reality.

About 20 people associated with the group have been detained. Three members have been tried and await judgment. And the rights lawyer who organized the guesthouse meeting, Xu Zhiyong, was indicted last month for “gathering a crowd to disrupt public order” and faces almost certain conviction.