Ganesh(Yogi) is a photographer who is in love with Sonu(Jayashree) for 2 years now. One the way back from a party with some of his college friends, they ram their car into a woman on the road. On Ganesh's insistence they drive away from the scene. They wish to forget the whole incident but some strange happenings convince them that they are being haunted by the ghost of the woman they hit.

Unlike movies in other genres, the chills in horror movies arise out of the build-up. Suspense about what is going to happen is usually what brings us to the edge of our seats. The lead-in to the "Boo" moment is just as important - sometimes, even more important - than the actual moment itself. The director has understood this well. So he keeps special effects to a minimum and concentrates on building up atmosphere and dread. That works well and many sequences, like the one where Jayashree visits the college library, succeed in generating real tension. Innovative camera angles and good music also help turn a darkroom into a rather scary place and it has been utilized well.

Sivi has a twist in the middle but it is hardly a surprise. In fact, the twist is almost disappointing since it leads to the story resembling other Tamil horror movies. But the director has a few surprises up his sleeve even after the twist and so the movie doesn't become completely predictable. Characters don't always say the truth and this helps add a few story layers that can be peeled back to surprise us.

Considering the topic, things would've been better left unexplained but the film tries to explain matters sometimes and gets on shaky ground. 'Nizhalgal' Ravi's explanation of spirits is silly and his 'proof' - photos with ghostly images - aren't very convincing. But such sequences are kept to a minimum and the movie retains its creepy atmosphere right upto the end without resorting to special effects for the sake of a big climax. The climax achieves the difficult task of being both low-key and surprising. It ties up some loose ends, answers a few questions and with a nice image to go along with that, it manages to be memorable both visually and in content.

Both Yogi and Jayashree start of shakily but get better as the movie improves. They spend most of the movie being scared and do that competently. Yogi is particularly good in the climax as he throws a challenge out there. Jayashree needs to improve her dialog delivery (she has too many pauses in her sentences) but is good otherwise. O Nenje... and Neruppum... are nice duets and the latter is also picturized well.