CHENNAI: Jason Sanjay's directorial debut Sigma revolves around Guru (Sundeep Kishan), a man who is drowning in debt. His immediate concern is saving his library, which is the last memory of his mother, but in this process, he gets entangled with mafia gangs, and finds himself with the key to a Rs 1,000-crore vault located abroad, containing the money of an underworld smuggler.

The mafia money, an illegally-operated underground casino beneath a theatre, and the race to secure the vault key — which is also connected to a pen drive containing crucial secrets — create an interesting premise for a heist flick, even though the template itself is quite familiar to us. The first half is largely devoted to establishing Guru and the crisis that pushes him into the mafia world. It also introduces gangster leader Vincent (Shiv Panditt), who is the primary antagonist, and his hired assassin Y (Yog Japee), as well as Kotlapati Veeraya Reddy (Sampath Raj), a drug kingpin and leader of a smuggling gang from another location — all of whom form a strong ensemble cast. Both criminal factions eventually find themselves pursuing the same object, which holds two separate elements that drive the conflict.

The second half brings all these characters together as the chase for the vault key turns into a race involving deceit, shifting loyalties and suspense over who will ultimately get their hands on the vault’s contents. There is plenty of action, colourful set pieces and humour in this portion, keeping the proceedings energetic. The climax is staged stylishly, although its impact could have been stronger had the plot been more tightly constructed and the story narrated with greater clarity.

But despite having such an elaborate setup, the screenplay struggles to sustain tension. The film leans on predictable tropes from Guru turning to gambling in desperation, losing to the casino owners and plotting his revenge, to a female character seducing an assassin to manipulate him into stealing the money and splitting it with her. Even scenes that have all the ingredients for excitement on paper fail to generate the necessary suspense and excitement on screen. The emotional dynamics between Sundeep’s and Faria’s characters are also underdeveloped, while Faria’s RJ Sam character is too underwritten to leave an impression.

However, Sigma manages to score on the technical front, with the cinematography by Krishnan Vasant, Thaman's music, and editing by Praveen KL complementing the scale of the film. The action, humour and colourful staging give it the feel of a commercial entertainer, even when the writing often doesn’t match the ambition of the setup.

On the whole, Sigma is an ambitious debut from Jason Sanjay, with a premise that offers considerable scope for a commercial action-heist film. However, the weak screenplay and predictable template prevent the film from making the most of its potential. The action portions and technical aspects make it engaging in parts, but the writing needed to infuse more freshness and create moments of greater tension to make the film impactful.