Farhan Qureshi and Raju Rastogi want to re-unite with their fellow collegian, Rancho, after faking a stroke abroad an Air India plane, and excusing himself from his wife - trouser less - respectively. Enroute, they encounter another student, Chatur Ramalingam, now a successful businessman, who reminds them of a bet they had undertaken 10 years ago. The trio, while recollecting hilarious antics, including their run-ins with the Dean of Delhi's Imperial College of Engineering, Viru Sahastrabudhe, race to locate Rancho, at his last known address - little knowing the secret that was kept from them all this time.
Who was Rancho?
Where did he come from?
Why did he leave?
Where is the original idiot now?
3 idiots answers all these questions while the friends are on a journey to find Rancho.