CHINA’S RULERS on Thursday offered a demonstration of the efficiency, ruthlessness and ultimate fragility of their regime. While the highest leaders secretively congregated in the seaside resort of Beidaihe, the wife of one of their closest colleagues was put on trial for murder in the provincial capital of Hefei. In a matter of hours, one loose end of a political crisis that began with the attempted defection of a police official to a U.S. consulate last February was tidily disposed of — or so the beachgoers hope.

“Trial” is a generous term to call the process for Gu Kailai and a household aide, who were charged with murdering a British businessman last November. Ms. Gu is the spouse of Bo Xilai, the former party chief in the city of Chongqing and a leading contender for a place in the ruling politburo before his purge a couple of months after his police chief’s attempted defection. Thursday’s proceedings, closed to all but a handful of outsiders, were conducted with blazing speed, considering that the trial was the most high-profile prosecution in China since that of Mao’s widow, Jiang Qing, 32 years ago. A conviction for Ms. Gu was seemingly assured by what The Post’s Keith B. Richburg reported was her admission of guilt.

There’s no telling if the version of events presented at the trial, in which Ms. Gu allegedly poisoned businessman Neil Heywood, a longtime associate, is true; the hurried, scripted process, in which Ms. Gu was denied her own attorneys, was hardly credible. But the men at Beidaihe were evidently less interested in judicial rigor than in preventing the trial from drifting into politically dangerous areas. One is the vast riches and apparently corrupt business dealings of the Bo family — a failing of numerous senior Chinese officials, reportedly including Xi Jinping, the new leader due to be appointed at an October party congress. Another is the populist agenda of Mr. Bo, who whipped up support in Chongqing by reviving Maoist slogans and songs.

With Ms. Gu disposed of, authorities will likely move on to Wang Lijun, the police official who triggered the scandal by fleeing to a U.S. consulate. Testimony at Thursday’s trial accused Mr. Wang of knowing about Ms. Gu’s murder plan. Mr. Wang surrendered to authorities in Beijing after speaking to American officials; it’s worth wondering whether in the absence of that leak Ms. Gu’s crime would ever have been revealed. Next may come Mr. Bo, whose fate will probably be determined not in a courtroom, but at the Beidaihe conclave.

By the time of the party congress, when Mr. Xi and a new politburo are installed, the Bo affair may be wrapped up, officially. But China’s leadership will have demonstrated — to the world and to its own people — its continuing disregard for the rule of law, its defiance of accountability and its fear of popular opinion. That’s a poor way to inaugurate a new leadership — which may find that the politics of purges and show trials is no longer sustainable.