Hastinapur may have been the largest and the most powerful kingdom in the land but it remained marred by succession crisis for three consecutive generations.
The first crisis came when Vichitravirya died without an heir. This was resolved by Vyasa impregnating his widows, Ambika and Ambalika.
The second crisis came when it was time to crown the two sons. Traditionally, the throne should have gone to Dhritarashtra since he was the older of the two. However, by virtue of him being blind, he is passed over for the able-bodied Pandu. Dhritarashtra is bitter about this but has no choice but to respect the decision of Bhishma and the council of Brahmins who decide on these matters.
The ultimate crisis – and the one that leads to the bloody war at Kurukshetra – happens when Kunti returns to Hastinapur with the five Pandavas. Even though Dhritarashtra has several years before his vanvass or retirement, rules demand that a crown prince be named. Yet again, Bhishma and the council of ministers, this time with an added player of Vidura to the mix, rule that Pandu’s son Yudhishthira be named the crown prince. This leads to a lot of discontentment in Dhritarashtra’s family. Not only is the blind king upset at not having his firstborn Duryodhana on the throne, the young Duryodhana is infuriated himself as he feels entitled to the throne.
In any case, Yudhishthira is named crown prince and Duryodhana starts plotting his revenge. His initial plan is to assassinate all the five brothers but in a manner that would make it look like an accident. So he hires the services of an architect called Purochana, who is also a minister in his father’s cabinet and a protégé of Duryodhana’s uncle Shakuni.
Purochana comes up with the idea of building a highly inflammable palace in Varanavat where the Pandava princes were due for a visit. However, the plan leaks to Vidura who on the day of their arrival warns Yudhishthira of the sinister plan in the form of a verse recited in a language that Duryodhana doesn’t understand.
In the meanwhile, Vidura also dispatches for the assistance of the Pandavas, a miner who single-handedly digs a long underground passage that starts at the palace and ends near the river Ganga. It takes nearly six months for the passage to be complete.
Throughout this entire time, Purochana is lurking in the shadows in the hope of finding an appropriate moment to set fire to the palace but fails to find one as Bhima would be awake all night. So he tries to poison the grains but also fails because Vidura sends mice into the palace and Yudhishthira realises the plot because the mice end up dead after eating the grain.
Finally, on the day of their escape, the Pandavas invite a Nishada woman and her five sons for a feast. In some accounts it is believed that they’re Purochana’s wife and sons. During the feast, they Pandavas get everyone intoxicated and then set the palace on fire themselves just before escaping from the secret tunnel. At the Ganges, a boatman sent by Vidura rows them to safety from where they go into hiding for a period of time. The only other person who is aware of the Pandavas being alive is Bhishma to whom Vidura reports the entire incident.
Duryodhana and Dhritarashtra mourn but are secretly happy and the former is made the crown prince.