It's a whodunit worthy of a Dan Brown novel: a small bronze plaque commemorating Thailand's 1932 revolution is ripped out from a very public place by parties unknown and substituted by one praising the Chakri Dynasty, whose 10th king took the throne in December. A disinclination by the authorities to find those responsible adds another element of mystery.
The original plaque, installed in 1936, marked the spot where a group of progressive army officers and civil servants proclaimed the end of the absolute monarchy in order to steer the country toward democracy.
"At this place, at dawn on June 24, 1932, we the People's Party have given birth to the constitution for the progress of the nation," is a translation of the words engraved on the brass disc.
The ideal still hasn't taken hold.A royalist military government that took power in a coup three years ago still rules Thailand, and its newly enacted constitution aims to limit the power of elected officials and give it instead to institutions traditionally associated with the palace, including the courts, the civil service and the military.
Prime Minister Prayuth Chan-ocha said last week that he has ordered an investigation into the plaque's disappearance, but warned against making a political issue of it.
He could understand why some people might be upset, he told reporters.
"But look at what we are doing today," he said. "Would it be better for us to look ahead at the future? Old subjects are just history."
The old plaque, about 30 centimeters (12 inches) in diameter and lying flush with the pavement, was embedded in Bangkok's Royal Plaza, a vast open area in the midst of government buildings and military installations.
It was so neglected as a landmark that its disappearance could only be estimated to have taken place between April 3 and 7.
As a symbol of democratic change, however, it was revered. For the same reason, it was despised.
Debate on social media over the plaque's disappearance has evoked a strong streak of antidemocratic sentiment, decrying the 1932 revolution for imposing unsuitable Western-style democracy causing corruption and all sorts of social ills; slamming the 1932 coup makers as evil; and even suggesting that the plaque was the physical incarnation of a curse on the nation.
Royalist resistance began almost immediately after the revolution, and slowly clawed back influence for the palace. By the late 1950s an accommodation was reached with the military, which sought its prestige, and by the late 1970s the constitutional monarchy was the country's most powerful institution, inviolable under the protection of the army.
This balance of power began to unravel in 2001, when billionaire populist Thaksin Shinawatra used his fortune to win an unprecedented electoral majority and become prime minister. Thaksin, accused of corruption, abuse of power and disrespect for the monarchy, was ousted by a military coup in 2006, setting off a sometimes violent struggle for power between his supporters and opponents, with the military strongly in the latter group.
Thaksin's opponents saw democracy as the problem, and some identified the 1932 revolution as the original sin.
"It seems to me that the junta has come to the view that the problems associated with Thaksin and erasing his regime involves a more deep-rooted issue of dealing with the notion of people's sovereignty that was embedded in the 1932 proclamation and first draft constitution," said Kevin Hewison, a senior research fellow at the Center for Southeast Asian Studies at Kyoto University.
"In this sense, the removal of the plaque is a symbolic act of delayed counterrevolution," he said.
Although a fringe group of ultra-royalists openly vowed late last year to remove or destroy the plaque, there is plenty to fuel speculation of a higher-level conspiracy.
Photos purportedly taken at the plaza during the period the plaque went missing show scaffolding at the spot, more suggestive of a public works project than a thief in the night. City officials asked to produce surveillance videos from the 11 cameras at the plaza say they were shut for maintenance during the same period. Police said they could not accept a criminal complaint of theft except from the plaque's owner, who was unknown. Pressed on the point, they threatened to sue an outspoken politician who suggested they weren't doing their duties.
Prime Minister Prayuth's suggestion that the case was a stone better left unturned was not idle advice. A government reform activist who sought to petition him on the matter was seized by soldiers and detained for 10 hours.
The plaque's removal also coincided with the signing of the new constitution by King Vajiralongkorn Bodindradebayavarangkun, who succeeded his late father, King Bhumibol Adulyadej, last year.
Ploenpote Atthakor, editorial page editor of the Bangkok Post, saw an upside to the affair.
"In the case of the ill-fated plaque, the silver lining is that its sudden disappearance has triggered an interest in this particular period of Thai history like never before," she wrote. "The people who removed it probably didn't expect that."