There is a strong whiff of filmmaking from an earlier era (the 80s and 90s) in Katham Katham. This is quite evident in the way the film begins, with a murder by the villain to establish his ruthlessness followed by the titles, which appear in the form of negatives of the scenes from the film (a style that was commonplace during the 80s).

The film then introduces its two heroes — Pandian (Natraj) and Nandha (Nandha). Pandian, an inspector who is in the pay of Periyannan, the local minister who runs in own government in the place. But he is no Saamy. He is so corrupt that traders shut shop on hearing that he is on the way to collect his 'dues' and has no qualms demanding sexual favours at the local brothel. Nandha is a straight arrow. He is idealistic and honest to a fault that he has been transferred 15 times in three years. In the scene when we first meet him, his father, who is also a cop (and has no misgiving in getting things for free), tells him to be pragmatic and bend a little.

What happens when these two characters are forced to endure each other? Naturally, there's friction but given that he is a subordinate, Nandha can only fume inside, because even the higher-ups to whom he complains about Pandian are Periyannan's stooges. The fact that Pandian walks away with all the glory when Nandha does good deeds only rubs salt into his wounded ego. However, Periyannan begins to mistrust Pandian following a scam gone wrong and makes an attempt on his life. Pandian survives and turns over a new leaf, vowing to bring him down but Nandha, not realizing his transformation, makes his own moves, including getting close to Periyannan, to get rid of his superior. Can he step back before his hatred for Pandian fully consumes him?

This is pucca masala material and Babu Thooyavan does a fairly good job with it until the interval point. And, Natraj, playing the role of an opportunist who reforms (something he did in his previous film Sathuranka Vettai as well), puts on a no-holds-barred performance (replete with Rajini mannerisms and double entendre dialogues) that complements Nandha's tightly wound-up act. But the film fails to pick up steam after Pandian's reformation. We expect sparks to fly in the confrontation between Pandian and Nandha, and Pandian and Periyannan but the script just fizzles out. There are no thrilling cat-and-mouse games and in their place all we get are predictable situations, a mood-killing love track between Nandha and Madhu, a local girl and a tame climax that is utterly disappointing.