Who's There? Kaun Hai Wahan? Is the story of a girl whose husband is haunted by her ex-boyfriend's ghost? Muskan (Kalpana Mathur) and Jay (Gagan Kang) love each other. But Muskan marries a rich businessman, Sunny (Rajbeer), at the insistence of her parents. Heartbroken, Jay consumes poison with the intention of committing suicide. Next, Sunny and Muskan, happily married, go on their honeymoon to a resort in Kerala. At the resort, Sunny starts seeing Jay's ghost in several forms as a dead body, as the non-existent watchman, as the taxi driver, etc. Muskan doesn't believe him but, nevertheless, wants to go back to Bombay as Sunny is delirious most of the times. She also starts experiencing strange things. Soon, they leave for the airport but miss the flight. As there are no more flights for a couple of days, the duo is stuck at the resort, where Sunny continues to see Jay's ghost.
Finally, when they are on their way back to Bombay by car, Muskan and Sunny are attacked by a group of goons who try to kidnap her. Sunny foils their plans. Back in Bombay, Sunny is still haunted by the ghost. One night, he finds Muskan romancing Jay's ghost in her sleep. For a change from all that's going on in their lives, the couple goes to the house of Muskan's parents. What happens there? Does Sunny find out about Muskan ex-boyfriend? What happens when Muskan learns that it is Jay's ghost that is haunting her husband? What were the exact circumstances of Jay's death?