Sahadevan (Dileep) is the son of a police constable Moolankuzhiyil Prabhakaran (Oduvil Unnikrishnan) who works in the dog squad, and Arjun is a trained police dog with a unique ability to nab culprits and decipher a crime scene. Sahadevan has only one ambition - to join the police department and for that he has cleared his exams and is waiting for the physical test, but he has an enemy, his own brother-in-law Peethambaran (Jagathy Sreekumar) who is hated by his family. Meanwhile, Baba(Sharat Saxena), a terrorist in jail plans to murder the CM Ravi Menon with the help of the current police commissioner, Gowri Shankar (Ashish Vidyarthi). This is because Ravi Menon is the man behind Baba's imprisonment. However Sahadevan foils the plan as his dog Arjun sacrifices himself while saving the minister from a time bomb, but survives. The blame is put on Sahadevan by Shankar but he is saved by the Director General of Police (Vijayaraghavan (actor)) who is his father's friend. Shankar, along with Peethambaram intentionally makes sure Sahadevan fails his physical test because he had found a way to foil the bomb plan in the hospital created to murder Ravi. When he finds out who the crooks are, he tries to find a way to foil it and that was to become a private detective via his uncle Karamchand alias Karunan Chanthakkavala (Captain Raju). Sahadevan becomes a private detective and calls himself CID Moosa, a short form of Moolamkuzhiyil Sahadevan. He has a funky car that can do tricks to assist him in evading his enemies. During all of this he falls in love with a girl named Meena (Bhavana (actress)). After numerous attempts, he makes her fall in love with him. Meanwhile, he managed to intercept the first terrorists who planned to place the bomb in the hospital. Shankar, in anger destroys Moosa's office saying it doesn't have license. When Moosa goes to Ravi for filing a complaint, Ravi's car explodes (as Baba's henchman had planted a bomb in it) and Moosa heroically saves him.