Kaththi Sandai starts off showing Jagapati Babu as a police officer in pursuit of a truckload filled with cash. During the chase, the truck gets involved in a fatal crash and the cop confiscates Rs. 50 crores which he hands over the government. Tamannaah plays a psychology student and is Jagapati Babu's sister.
As the story progresses, we are introduced to Vishal who is hell-bent on winning Tamannaah's heart as he is head over heels in love with her. He goes on to win her heart with sweet tricks and thrills along with the help of Soori and his assistants. After Tamannaah tells Jagapati Babu that she wants to get married to Vishal, he does a thorough background check to verify whether he has a good reputation and can be trusted. Once he is sure, Vishal and Tamannaah get engaged.
At this point, Jagapati Babu is abducted by a group of people who then threaten him to hand over the money that he confiscated for himself without revealing to the government. The group threaten him that if he were to not co-operate his family would be in grave danger. Soon, Vishal gets a phone call and is instructed to unearth money from the bathroom tiles and bring it over to an undisclosed location without informing anyone. However, Vishal has other plans in mind and thrashes the goons to save Jagapati Babu.
After rescuing him, Vishal reveals that he is indeed a CBI official and that Rs. 250 crores from the truck crash was missing which he has been investigating. He tells him that he had gotten close with his sister to find out where all that money went. Then, we are introduced to the antagonist Tarun Arora who also is in pursuit of the money and reveals that Vishal is a poser and was in jail with him. He states that Vishal overhears his theft plan and is now fooling everybody. Meanwhile, Tamannaah realizes that Vishal has been cheating her this whole time and problems crop up in their relationship.
Tarun Arora and Jagapati Babu then go in search of Vishal who ends up in a small accident which makes him lose his memory. They then bring in Dr. Boothri played by Vadivelu to revive his memory and get the money. How the film progresses from this point on, whether the villain gets the money, how Vishal makes amends with Tamannaah forms the rest of the plot of Kaththi Sandai.
In comparison to previous Suraj films, there are moments in Kaththi Sandai that make you laugh, but not too many laugh out loud moments. The director has done a commendable job when it comes to filming action sequences and crafting the comedy tracks in the film.
Vishal has performed his role well proving he can shoulder a film forward. He does well in action, comedy and dance. However, he needs to work on his expressions more. Tamannaah scores in the glamour department as well as in acting. Her Baahubali experience is clearly visible as she hits the rights notes when it comes to expressing herself. Jagapati Babu and Tarun Arora have performed their roles amicably.
Soori provides quite a lot more laughs than many would have expected in the first half of the story. 'Vaigai Puyal' Vadivelu's entry in the second half gets a tremendous response and the veteran comedy superstar does what he sets out to do.
The story could have been a clear winner had it been written with more care and a tighter screenplay. Stunts in the film are commendable. Richard M. Nathan deserves a pat on the back for his cinematography; especially in the song sequences. Hiphop Tamizha's songs are average with the exception of the chart-buster "Naan Konjum Karuppu Thaan". He is proving himself to be an able composer in the background score department though.
In short, Kaththi Sandai could have been sharper.