In a makeshift air-conditioned cabin behind the stage, amid blankets and pillows scattered on the floor, a senior leader of the red shirts bluntly spelled out his response to anti-government protest leader Suthep Thaugsuban's latest move.
"Monday, May 13, is the most important day, as the presidents of the courts must decided whether to accept the proposal of Suthep Thaugsuban," said Dr Weng Tojirakarn, referring to the leader of People's Democratic Reform Committee (PDRC).
"If they do, they will destroy (all faith in) the judicial system.
"We will not accept an unconstitutional prime minister, no matter what."
The PDRC has essentially seized Government House, the seat of the prime minister. On Saturday afternoon, Suthep declared the government led by the former prime minister Yingluck Shinawatra's Puea Thai party as having failed.
He urged the newly-appointed Speaker of the Senate and top officials of Thailand's judiciary, to name an appointed prime minister on Monday.
If they would not, the PDRC would take the matter into their own hands, he said ominously.
From Monday, Suthep will be making his announcements from Government House, long abandoned by Ms Yingluck and her erstwhile cabinet, and watched over only by a few police and army soldiers who have allowed Suthep free access.
Across the city, at its western edge, right by one of the palaces of the Crown Prince, are the United Front for Democracy against Dictatorship (UDD) red shirts who support the beleaguered caretaker government. Ms Yingluck was disqualified from office last week by a court, incensing the red shirts who say they will not tolerate what they - and many independent analysts - call a "judicial coup."
Late on Saturday evening, on the stage in the hot and humid night, before an enormous backdrop which read "Fight for Democracy" and "We want Election" red shirt activists were belting out a song.
Two of them, with buffalo yokes around their necks, danced wildly, pumping up the enormous crowd that formed a small sea of red.
The red shirts, many from farming communities of the north and north-east, have effectively turned the wooden yoke of a buffalo - the derogatory term used for them by supporters of their royalist enemies the PDRC, into a symbol of defiance, pride, identity, and the class divide between the old money Bangkok elites and the upcountry masses.
The almost decade-long conflict pits Bangkok's old elites and royalist middle class, and conservative Democrat Party supporters, against the populist billionaire Thaksin Shinawatra and his supporters. Many royalists see Thaksin, Ms Yingluck's older brother who lives in self-exile after dodging a two-year corruption sentence, as a corrupt closet Republican who buys his way to power through manipulated elections.
The power struggle for control of the country's future, is also shadowed by another more opaque issue - the looming royal succession. King Bhumibol Adulyadej who has reigned for more than 65 years, is a frail 86 and many Thais are anxious about an uncertain future without him as the Kingdom's final moral authority.
The red shirts which helped sweep Ms Yingluck to power in 2011, see the regular sabotage of Thaksinite governments as a conspiracy of the elites and their institutions, to maintain Thailand's old top-down feudal social structure and deny the masses their electoral choices.
After the dancing and singing, UDD leader Jatuporn Promphan took to the stage. "We want to change this country, but we want to do it through elections," he said.
It was more a warning than a statement. Earlier, speaking to reporters, he said an unelected prime minster would be unconstitutional, unacceptable, and push Thailand down the road to civil war.
Backstage in the air-conditioned cabin, UDD leader Thida Tawornseth said in an interview: "We want to warn the courts, and also the president of the Senate, and the Election Commission."
The PDRC wants to "eradicate" the Shinawatra family from Thai politics and is pushing for an appointed government which would undertake deep reforms before allowing another election.
But the PDRC was not interested in real reform, Ms Thida contended.
"They want to freeze the country," she said. "If they get a new, appointed prime minister, they will freeze the country for three to five years. They will hold off elections, and they will rewrite the constitution."
The UDD, while mobilising supporters to send a signal to the courts and those in the establishment elites who back the PDRC, seems to be playing a waiting game, with the conservative leadership asking more radical elements to be restrained.
More than 25 have been killed, and several hundred injured, in clashes and almost daily bomb and shooting attacks, through the roughly six months of Thailand's political crisis.
There is almost no middle ground in Thailand's conflict. And as the deadlock continues and becomes more acute, an escalation in the violence is a constant danger.
Late on Saturday night, two M79 grenades landed and exploded near Government House, injuring two supporters of the PDRC-allied Students and People Network for Thailand's Reform, itself seen as a radical group.