C.I.D Moosa is a 2003 Indian Malayalam-language action comedy film directed by Johny Antony, written by the script-writing duo Udaykrishna–Sibi K. Thomas, and co-produced by Dileep. It stars Dileep in the title role of a private detective, and features an ensemble cast of Bhavana, Ashish Vidyarthi, Sharat Saxena, Murali, Harisree Ashokan, Cochin Haneefa, Jagathy Sreekumar, Vijayaraghavan, Captain Raju, Oduvil Unnikrishnan, Sukumari, and Salim Kumar. The film follows Moolamkuzhiyil Sahadevan, popularly known as CID Moosa, a young man from a police family who sets out to prove his worth as a detective while uncovering a terrorist plot.

The film was released in 4 July 2003. It was a box office success, becoming the second highest-grossing Malayalam film of the year, behind Balettan. Known for its slapstick comedy, it has developed a cult following. C.I.D Moosa was remade in Tamil as Cheena Thaana 001, in Kannada as CID Eesha and in Telugu as Ramachari. A sequel has been rumoured to be in the works by the makers.

Moolamkuzhiyil Sahadevan is the son of a police constable named Prabhakaran, who works in the local police department's dog squad; their dog Arjun a German Shepherd is a trained member of the squad with a unique ability to nab culprits and sniff out clues. Sahadevan has only one ambition: to join the Kerala Police department for which he clears his exams and prepares for the physical test. However, Sahadevan is not on good terms with his brother-in-law Pitambaran (who too is a Sub-inspector in the force) since he married Sahadevan's elder sister after an elopement.

Meanwhile, a terrorist leader named Khalid "Baba" Muhammed, who is incarcerated in the Tihar Jail, formulates a plot to murder the new Chief Minister of Kerala Ravi Menon with the help of a shrewd and corrupt Police Commissioner Gowrishankar. Menon previously served as the Union Minister of State for Home Affairs who ordered for the quelling of Baba's terrorist organization, which led to Baba's imprisonment and the slaying of his family. Baba and Shankar arranged 3 terrorists Randheer, Amar and Jandu to implant a bomb inside the hospital where Menon is undergoing treatment, but Sahadevan and Arjun find the bomb and throw it out before it explodes, though Arjun ends up being injured. Despite this, Sahadevan is able to arrange medical treatment to restore Arjun back to full health.

In response to Sahadevan's actions at the hospital, Gowrishankar (with help from Pitambaran) intentionally makes Sahadevan fail his physical test. Sahadevan is at first dismayed and discouraged, but considers becoming a private detective and following the footsteps of his uncle 'Karamchand'. Karamchand willingly leaves his office and tools to his nephew, and Sahadevan adopts the pseudonym CID 'Moosa' (from the first syllables of his first and last names). In his first assignment, Moosa and his associates take it upon themselves to investigate the attack on the CM, and manage to nab Randheer (who planted the bomb at the hospital) and surrender him over to the police, impressing the DIG Sathyanath (who happens to be Menon's nephew).

However, Gowrishankar secretly kills Randheer to avoid an interrogation, and destroys Moosa's office after learning that the firm doesn't have a license. The remaining two terrorists then plant another bomb on Menon's car in an attempt to kill him, but this is foiled when Moosa tries to meet Menon to file a complaint about the office ransacking, saving Menon from being killed by the explosion. Moosa then deliberately decides to not complain, to earn false praises by the public and Menon as the hero who saved the CM's life. Upon hearing what has happened, Baba furiously breaks out of prison as he personally intends to help Gowrishankar, Amar and Jandu in finishing off both Menon and Moosa. After some false leads involving a local lunatic who gives Moosa the run-around several times, Moosa later finds Amar, recognizing him as the second terrorist who planned the bomb at the hospital along with Randheer.

With that in mind, Moosa tries to nab Amar, but accidentally kills him by shooting him in the head. This puts him in trouble, as he was told by Sathyanath only to shoot below the knee or he would face criminal charges. However, Sathyanath learns that the Central government issued a reward of ₹ 5 lakhs for Amar's head which Moosa will receive, much to the commissioner's dismay. In the meantime, Meena, who Moosa relentlessly tries to woo without success, informs him that Randheer, Amar and Jandu were paying guests in her apartment, and that she filed a complaint to the commissioner as Randheer and Jandu were absconding. However, upon being told by Moosa that they were terrorists and they were murdered by Gowrishankar, Meena ends up being arrested by Gowrishankar under the false charges of harbouring terrorists.

Moosa tries to plead for Meena's innocence to Gowrishankar by stating that she was unaware of the terrorists' identities, but he refuses and takes Meena into custody. As Gowrishankar tortures Meena, he tries to molest her, but Moosa arrives to the rescue by thrashing him before releasing Meena, who reciprocates her feelings to Moosa in return. Because of this, Gowrishankar issues an arrest warrant on Moosa approved by a reluctant Menon. Before the arrest comes to pass, Moosa sneaks into Menon's house to plead his innocence to Menon, who unsurprisingly states that he already knows it by admitting that he witnessed Baba walking on the road on his way home, and is sure he's behind the attacks.