Arjun's(Govinda) small world of happiness consists of lovable father, brother(Rahul Roy), sister-in-law(Farha), brother-in-law(Dilip Tahil) and a lawyer-friend Sagar (Paresh Rawal) who masterminds their prospering business.
Into Arjun's life walks inPooja(Manisha Koirala) who brings love, but soon things would start going wrong. An attempt is made on Arjun & Pooja's life. They are saved, but in a freak incident Arjun's brother is killed by his wife Madhu(Farha), but Pooja is convicted. Arjun's problem are compounded when he helps pooja escape from prison. Close on the heels of this tragedy, another one follows. Arjun and Pooja have to solve this mystery as it involves close and dear members of the family and friends.
Now Arjun and Pooja on the run from law, must solve the mysteries before they too become victims of this mastermind. Songs, thrills, action, emotions are what keeps ACHANAK(SUDDENLY) always one step ahead of its audience.