No. 20 Madras Mail

The No.20 Madras Mail departs from Trivandrum Central with R. K. Nair, his wife Geetha, and daughter Devi in the first class coach. Tony Kurishingal and his friends board the same coach from Kollam, while Sunil boards later at Ernakulam Town. The crowded carriage immediately sets up a mix of flirtations, schemes, and simmering tension for the long journey ahead.

Tony and his friends try to secure a seat in Devi's coach, sparking heated exchanges with Nair and Sunil. Film star Mammootty boards the train from Thrissur and ends up in the same coach, intensifying the mix of authority and charm aboard. The stage is set for a journey where flirtations, bravado, and danger intertwine.

Nadar, the ticket inspector, stays with Tony for a while and then leaves the train at Palakkad. Chokalingam (Choki) becomes the new TTE, taking charge of the carriage. Tony and friends quickly realize the new guard changes the dynamics onboard.

Tony and his friends visit Mammootty aboard the train and form an unexpected friendship with the film star. Their bond brings a momentary peace to the otherwise tense journey. Devi remains in the background as the source of their ambitions and anxieties.

Tony tries to flirt with Devi as she returns from the restroom, which puts him at odds with Nair. Mammootty intervenes to calm the situation and restore some order. The incident intensifies the underlying suspicions on board.

In the morning, as the train approaches Madras, Devi is found murdered in the toilet. Tony and his friends become the main suspects and flee to avoid arrest. The journey suddenly turns from entertainment to a criminal mystery.

DySP Murthy begins the investigation and learns from Choki that Mammootty had taken photos of Tony and his friends in the coach. The photos are publicly displayed, inflaming a case of mistaken guilt. Mammootty helps Tony and his friends sneak back to Kerala, convinced of their innocence.

Back home, Sunil corners Tony, Hari, and Kanjikkuzhi at a lakeside and tries to murder them, thinking Devi's killer is among them. Tony overpowers Sunil in the fight and compels him to spill information about Devi's killer. The truth begins to emerge from the confrontation.

Sunil becomes an ally and reveals that Devi left a diary with Sr. Gloria. From Gloria, they learn that Devi entrusted the diary before going to Madras, and that Nair is connected to her past. The diary deepens the mystery and points toward the killer.

Armed with Devi's diary, the group discovers that Nair is Devi's killer. Tony impersonates Mammootty's voice to contact Nair and demands ₹20 lakh in exchange for the diary, coordinating the plan aboard the train on a Wednesday.

Nair travels to Salem by taxi to recover the diary, but Tony boards the train mid-journey and, with Mammootty's help, overpowers Nair's henchmen. Nair re-enters the train at Salem and confronts Tony. The chase tightens the net around the killer.

The next morning in Madras, DySP Murthy arrests Nair after he is confronted and forced to confess. Nair reveals that he killed Devi when she discovered his involvement in her father's murder. The revelation finally brings Tony's group vindication.

On No.19 Trivandrum Mail, Tony, Hari, and Kanjikkuzhi head home, having cleared their names. Mammootty appears again on the same train, and Tony's group welcomes him as they promise a safe and peaceful journey back. The trip ends with them returning to their lives in Kerala.