Diary

A couple on their honeymoon travels along the Ooty ghat roads and at the exact 13th hairpin bend their car crashes. The incident foreshadows a haunting that threads through the rest of the story.

A fresh S.I., Varadhan, is assigned to solve a long-unsolved murder case from Ooty as his first assignment. He revisits the case file with Pavithra, interviews the officer who investigated 16 years ago, and begins mapping the clues around the jewelry that was reported missing.

He checks with other stations for similar robberies and discovers patterns that link several cases to the Ooty murder. These connections push Varadhan to pursue the trail beyond his own station.

A batchmate in Coimbatore informs him of a similar jewelry robbery in Kumbakonam and identifies a suspect. Varadhan decides to chase the lead in person, bringing Pavithra along.

They trace the carjacker Satya through CCTV and head toward Coimbatore, only to find the station car missing after Satya allegedly escapes with Varadhan's service gun. The chase continues along the ghats in a police jeep.

The last Ooty bus departs at midnight toward Coimbatore with a mix of passengers, including an eloping couple. The robbers eye the jewelry as the journey unfolds, while a tribal ceremony offers the lovers some protection.

Onboard, uneasy passengers sense something supernatural, while a young man and an old lady feel uncanny presences. Varadhan and Pavithra join the bus to observe and piece together what is happening.

Varadhan confronts Satya on the bus and recovers his gun after a scuffle. He then subdues the robbers attempting to loot the runaway couples and ties them up, stabilizing the tense situation.

Pavithra checks hotels and transport records on the ground and discovers the bus number Varadhan provided does not exist. She learns the last Ooty bus has already reached Coimbatore, deepening the mystery.

Gunasekaran's henchmen catch up and attack the passengers as the driver is fatally injured. The bus crashes into the gorge at the 13th bend, with Varadhan, the eloping couple, and a few others surviving.

Rescuers uncover the wreck and skeletons inside; Varadhan explains the Bus 375 urban legend and the ghosts that ride it every cycle. The realization dawns that the honeymoon murder is the same case Varadhan is investigating.

Varadhan and Pavithra conclude that the haunted bus travels the route periodically and that leaving before the bend ensures survival. They verify the missing bus's identity with the transport department, confirming the spectral rider theory.

With circumstantial evidence tying him to crimes from 16 years ago, Gunasekaran is arrested. The authorities piece together his motive and the link to the ghosts’ hauntings.

In the epilogue, Varadhan learns the prologue car was driven by his father and that his parents died at the 13th bend. Four years later, Varadhan and Pavitra are married, and they realize the bus travels every leap year on Feb 29, with Satya boarding it to see his mother again.