Sam (Emraan Hashmi) and Mahi (Nikita Dutta) have been married for a couple of years against the wishes of the latter's parents, an issue that neither is happy about, and remains as a jagged edge. So when Sam gets an opportunity to develop the nuclear energy plant in Mauritius, he is excited that they may be able to rekindle the romance, whilst Mahi is somewhat uncertain about leaving all her friends and family behind Mumbai. When they arrive in Mauritius, they get a massive bungalow to live in, and Mahi's problems start as soon as she unwittingly buys a Dybbuk, a box that contains a secret, perhaps a curse from the past, that will be released as soon as the box is opened.
There's no point buying a box and not opening it, hence Mahi does the needful unknowingly and a malevolent spirit possesses the family. Mahi starts doing strange things and Sam is forced to seek advice from the Church first, and then from a Rabbi played by Manav Kaul to help them return to normalcy.
The rest of Dybbuk is rather formulaic, as the good must triumph over evil, but not without our learning why the alleged evil is what it is, and why it is tormenting Sam and Mahi, who seem to have accidentally crossed its path to vengeance against the entire island. The spirit is intelligent and educated enough to know that Sam is in charge of the operations of the nuclear reactor, which, with the use of recently acquired Plutonium can devastate the whole island. Dybbuk is occasionally startling, but cannot sustain the horror it is meant to, and the SFX of the evil spirit is quite similar to Vikram Bhatt movies. Emraan Hashmi is the natural choice for the lead as he is a sleepwalker through the role he has done umpteen times before this. Nikita Dutta is likeable in her plight but her troubles don't evoke enough sympathy. Dybbuk is an average fare and will be lost in the crowd of another not so scary "horror" movie.