Inspired by the Italian Giallo genre of films. 100 Days uses main plot elements from Lucio Fulci?s 1977 classic "Sette note in nero" (Released as Seven Notes in Black & The Psychic).
The film opens with a young woman, Devi (Madhuri Dixit), who gets sudden visions (usually accompanied with a mild panic attack) of incidents and accidents that are yet to happen. Devi has a vision of her sister Rama (Moon Moon Sen) being murdered. Her college friends Sudha (Sabeeha) and Sunil (Javed Jaffrey) try to help her sort through her visions but to little avail.
Devi is relieved after she talks to her sister & finds that she is alive. However, just some time later, Rama is murdered the same way Devi pictured. The murderer buries Rama?s body in a closed mansions wall. Rama is reported missing. Devi firmly believes Rama is dead. Five years later, Devi moves to her uncle?s(Ajit Vachani) home where she eventually meets and is courted by millionaire businessman Ram Kumar(Jackie Shroff). Sunil, who was secretly in love with Devi, is disappointed. Devi & Ram marry & enter his family mansion, which he has re-earned after a legal battle. Little known to anybody, even Devi, this is the same mansion where Rama is buried. But when Devi starts having the visions again, Rama?s skeleton is not the only thing that will come tumbling out.
Devi starts getting visions again. She sees a wall in the mansion being torn down. Devi tears down the wall, only to find a skeleton tumbling out of it. Devi knows who the skeleton is: it is Rama, since she had a necklace similar to Devi?s on her body. Also, the woman is roughly same height as that of Rama. The Inspector(Shivaji Satam) quickly points out that since the mansion was closed when Devi disappeared, anyone could have snucked a dead body in there & nobody would know the truth. However, he doubts that the woman is Rama: Several such necklaces are available.
Devi now gets another vision of another woman get murdered. She also pinpoints two details: a magazine cover with a horse on it and a video cassette labeled 100 Days. Sunil and Devi visit the magazine office. The editor politely informs them that the next six months? covers do not feature any equestrian theme whatsoever. The cassette clue, too, is a dead end: no video store in Bombay carries any such title. Devi begins delving into Rama?s life. Rama was a research scholar; she was working on a thesis about ancient sculptures and temples in India. A quick investigation by Devi reveals that many artifacts listed by Rama either mysteriously disappeared, got stolen or were replaced by fakes. She also learns that two people working in the museum, Jagmohan & Parvati were fired on the suspicion. Parvati is revealed to be the new victim of Devi?s visions.
Jagmohan is a hot headed man while Parvati knows the killer of Rama. Parvati has videotaped the murder & knows the murderer. She tries to blackmail the murderer, but the murderer tries to kill her. She sneaks into a video library, sticks a tape on the cassette, names it 100 Days & tries to escape. But Jagmohan succeeds in killing her, just as Devi had seen. Later, due to some last minute developments, the magazine prints an issue with a horse on its cover. Devi soon realizes that Parvati has been murdered. She goes to the video library & retrieves the tape. Jagmohan tries to kill her, but her luck prevails. She comes back into the mansion, where she gets a vision of herself in an injured state & a broken mirror in the mansion. She tells Ram about the developments & sits with him to watch the cassette. Ram has no idea about the cassette?s contents.
However, as the cassette is being played, Devi gets another shock: she sees Rama confronting Ram. Based on the evidence in the cassette, it becomes clear that Ram is the murderer. Devi tells him that she is pregnant with his child. Ram offers to explain. Ram tells that all his relatives fought for money all these years, leaving him alone. Soon, he took to illegal ways of earning money. He ran into Jagmohan & Parvati. Later, the trio started smuggling the artifacts. Rama suspected it & decided to expose them. That night, Ram went to talk to Rama. But Jagmohan, who lost his temper, killed her. Parvati was secretly taping the incident, but due to her camera?s angle, it looked as if Ram was the killer. Ram offers to surrender to police & calls them. He confesses his crimes & asks them to arrest him.
No sooner has he stopped talking, than Jagmohan hits him on his head with a shankh(conch shell). Ram collapses unconscious, while Devi fights Jagmohan. In this unequal fight, Devi is overpowered & rendered unconscious as well. Jagmohan buries them alive in the same wall where he buried Rama. Just as he is about to escape, he sees Sunil coming in. Jagmohan hides while Sunil is surprised to see the mansion open with nobody in it. Just then, Devi?s wrist watch chimes. Sunil is surprised to hear the sound coming from the wall & puts two & two together. He starts digging the wall, thus saving the unconscious duo. Jagmohan suddenly attacks Sunil. However, Sunil puts up a good fight with the enemy with an unfair advantage. Ram wakes up too & soon overpowers Jagmohan with help of Sunil.
The police arrive on the scene. Sunil is surprised to see Ram being arrested as well. Devi looks wearily as the police vans go away.