Diary is a horror - thriller film written and directed by Innasi Pandiyan, and produced by Kathiresan under the banner Five Star Creations. The film has Arulnithi and Pavithra Marimuthu in the lead roles while Sha Ra, Jayaprakash, Kishore and others play supporting roles. The cinematography is handled by Aravinnd Singh and the music is composed by Ron Ethan Yohann.

Varadha, played by Arulnithi, is a newly recruited Sub Inspector in the police department. Each SI is given the task of choosing an unsolved case and solving it. Varadha's choice lands him up in Ooty, where he is assisted by Pavithra. On the other hand, the last bus from Ooty to Coimbatore leaves with very few passengers, and some of them start experiencing paranormal things. How the case related to the bus is what Diary is all about.

The way in which Diary starts off is intriguing and keeps us glued to the screen till a group of dacoits are introduced. The dacoits enter hotel rooms, kill couples and take away their gold, it holds our attention really well and keeps us on the edge of our seats.

But then, when the film switches to the bus portions, the pacing slows down rapidly. We start wondering where the film is headed, till the pre-climax sequence. The bus portion is where the horror elements kick in and they could have been written far better than just resorting to jump scares. The effort to genuinely evoke fear seems missing.

Arulnithi, despite being a part of so many thriller films, makes sure his character stands out here as well. It is a great skill to act in a number of similarly written roles, yet make sure each one is different. Debutant Pavithra Marimuthu also shines in the limited space she is given, and is someone to watch out for in her upcoming movies. The supporting cast do not have much scope to make an impression but generally none of them look amateurish at any point.

The dialogues in Diary are a perfect mix of brilliance and preachiness. The cleverness makes you applaud for a few scenes while the preachy/motivation quote type dialogues tire you. Ron Ethan Yohann's background score is highly effective and provides goosebumps in the thriller portions. But the same cannot be said about the songs, which are passable. The cinematography by Aravinnd Singh is impressive in the flashback sequence and gives the film what it exactly needs during the present day portions.

Overall, Diary could have been a far better film based on the potential the script had. But the tonal shifts between horror and crime thriller needed to be smooth, which is where the film mainly falters. It is one of those films where the audience knows exactly how better the film could have been, and feel genuinely sad that it didn't come out that way.