Jealous of Duryodhana

Bhishma, Dronacharya, and Vidura called a meeting to designate the next king, in place of Dhritarashtra. Two options were discussed. First, Yudhisthira being the eldest of the Kuru princes was considered for nomination. Second view, supported by Dhritarashtra and his brother-in-law Shakuni (brother of his wife queen Gandhari and maternal uncle of Duryodhana) was to select Duryodhana as the future king. But the opinion of Bhishma, Dronacharya, Kripacharya (Guru of the Royal House), and Vidura of nominating Yudhisthira as the heir-apparent prevailed.

Jealous Duryodhana Plans to Kill Pandavas
This naturally caused huge disappointment in Duryodhana's camp. Uncle Shakuni was well known for his villainous nature and cunning. He was displeased with the fact that his nephew Duryodhana was denied the chance to become the king. For this purpose in particular, he had come to stay at Hastinapur. He was well aware of the value and power of a king. Therefore, he lost no opportunity to humiliate and even to attempt to kill the Pandavas.
Soon the desired opportunity came to the evil minded Duryodhana and Shakuni to put an end to Pandavas.

Palace of Lac (combustible material)
In nearby town of Varnavata, a grand exhibition used to be arranged every year. The organizers always sent an invitation to the King of Hastinapur to send some members of Royal Family to grace the occasion. This time, Duryodhana and Shakuni persuaded Dhritarashtra to send Pandavas to Varnavata. The king agreed, and accordingly Pandavas were informed. Yudhisthira and brothers were also happy to get the opportunity to mix with the people of their kingdom and get first hand information about their problems or wellbeing.
Therefore, accompanied by their mother, Kunti, Pandavas decided to attend the exhibition at Varnavata.
As was customary, the organizers decided to build a temporary palatial house for their stay. The job was entrusted to one expert contractor whom Shakuni knew very well. Bribing the fellow, Duryodhana and Shakuni deliberated a secret plan to put an end to the life of Pandavas. It was decided that the palace that would house the Pandavas should be constructed out of highly inflammable material like Lac, resins, hemp, oil, fat, etc. the contractor completed his job very meticulously and it was not possible to detect any foul play from cursory outward examination of the house
. Duryodhana and uncle Shakuni arranged to send their secret agent in guise of a servant who was instructed to put the house on fire when Pandavas would be fast asleep. Death due to burns would appear as an accident.
Thus plan was sure to succeed had the spies of Vidura, the Prime Minister and well wisher of Pandavas, had not told Vidura about the same. Vidura, on his part, alerted the Pandavas about the 'death trap' and a solution was offered in the form of digging an underground tunnel in advance to fool the Kauravas. The tunnel opened in far off forest.
The house was torched as planned and it burnt to ashes within no time. Pandavas had already left through the tunnel, but five workers and servants were charred to death. Everyone, including the Karna, took Pandavas to be dead.
The narrow escape put Kunti in a state of shock and apprehension. She could not put her sons at the mercy of Duryodhana and Shakuni. She was afraid they would again make attempt on their lives. Therefore, she pleaded with her sons to live incognito for time being.
Accordingly they stayed in the forest for a few days.