Ek Deewaana Tha follows the story of Shiv (Namik Paul) and his love for Sharanya (Donal Bisht) . One day, Shiv dies in a mysterious accident and Sharanya briefly slips into a coma. When she wakes up, she has no memory of the last two years.
Vyom Bedi (Vikram Singh Chauhan), who claims to be Sharanya's boyfriend, assures her that he will bring back her memory. Shortly, strange incidents happen around Sharanya who begins to feel the presence of an entity around her. This entity keeps hurting Vyom both physically and mentally. Odhni (Delnaaz Irani) warns both the families but gets into trouble. Vyom's father, Rajan Bedi (Amar Upadhyay) has his own secrets as he had committed a crime two years ago on the day of the solar eclipse.
Sharanya meets a "sadhvi" (Shilpa Tulaskar) who tells her that she must marry her boyfriend in order to protect him from an evil spirit before the next solar eclipse. Sharanya agrees to marry Vyom angering Shiv's spirit. But eventually, Sharanya's father was killed by Rajan Bedi as she and Vyom get married.
After their marriage, Detective Freddy(Jason Tham) gets to know the mystery behind Shiv's death and Rajan Bedi. But he gets stabbed by someone when he was going to tell the truth to Sharanya. Shiv's spirit injures vyom very badly in order to separate them. Sharanya goes to kapali hills in order to know the truth. But when she goes there, she finds Shiv's dead body and remembers everything from the past five years. She comes to know that Shiv was her actual boyfriend and they were deeply in love with each other.
In college, Vyom was obsessed with Sharanya. He even proposed to her but she rejected him. He then killed Shiv and injured Sharanya in order to marry her.Now Sharanya is trying to collect evidence against Vyom with the help of Shiv in order to give Shiv justice.Meanwhile, Vyom murdered Vidyut & Sadhviji. He also came to know about Shiv's spirit and Sharanya's awareness about his reality.
Sharanya suspects Vyom and collects all the proofs which goes against Vyom and tries to disclose him in between the party but in vain as Madhvi takes all the blame and remembers that what all proofs she got were indirectly provided to her to confuse her. Police takes Madhvi under arrest. When Rajan gets to know that Madhvi is behind the bars he gets in real rage and asks Vyom to either get Madhvi out of the bars or he will disclose him in front of everyone. Vyom again plans everything with freddy and kills his father Rajan(which was again a plan) and puts all the blame on his father and hence Madhvi is out of jail.
Vyom plays another game with freddy and blackmails Odhni to show him some way to get rid of Shiv's soul and Odhni says Vyom to burn all Shiv's belongings along with Shiv's body. Odhni warns that if Shiv's single belonging will be left behind then he will come back. Odhni (being blackmailed by Vyom) convinces Sharanya to perform Shiv's final rites so he can move on which she does. Vyom gains Shiv's mother's trust too and she also suggests Shiv and Sharanya to move on. Sharanya reluctantly agrees and hence they burnt Shiv's corpse and everything that belonged to Shiv.
While going back to bedi house freddy calls Vyom, Vyom stops the car and moves out to talk to him asking Freddy to kill odhni too. While they were on roadside Sharanya accidently sees Rajan and Madhvi in a car passing by.she gets out of the car to say that she have seen them. She tries to convince him but Vyom tries to talk out of it and Sharanya pushes Vyom back, gets on the driving seat and stops the car exactly in front of Rajan and Madhvi's car. Vyom comes and tries to explain sharanya but she slaps him scolds him.
Finally, Vyom reveals all the crimes he did (he killed Shiv's father in order to protect his parents, he killed Sharanya's father and Sadhvi, as they both found out Shiv is her lover, not Vyom, also he killed Shranaya's doctor and many others). Vyom accepts that he stabbed Shiv and killed him and accepts all the murders he have done in madness of her love. Sharanya says that he will never get her love and leaves him saying he is a big fraud but stops on Shiv's mother's choking voice. Vyom says that he have murdered many and killing her is no big deal for him. Sharanya stops and says that she will listen to what he says and asks him to leave Shiv's mothers neck.
They reach home and Shiv's mother whispers her to runaway and don't suffer here. Shranya escapes from the Bedi's house and Vyom chases her into the jungle. Shranaya calls for Shiv, (as she gets a devi murti along with shiv's engagement ring ie; Shiv's belonging which was covered in a red cloth which sharanya's father was trying to run with but was murdered by vyom) and he returns.
He beats up Vyom as soon as he was about to kill him Rajan comes with Madhavi and points a gun at Shiv's mother head. Rajan tells Shiv to let go of Vyom or he will kill his mother. Shranya holds Shiv's ring which he was gonna propose with. Vyom says "give me the ring or else dad will kill Shiv's mother". As soon as she is going to remove the ring, Shiv's mother pushes Shranaya down a cliff and she dies. Finally, Shranaya becomes a ghost and joins Shiv in the afterlife. Vyom is about to kill Shiv's mother but instead kills himself.
Twenty-five years later, after the death of Vyom and Sharanya, Rajan and Madhavi are shown to have raised a child named Shivani (Shivani Surve) as her own daughter. She comes back from London to the Bedi's house, 8 years later. She doesn't remember anything that happened 20 years ago. She introduces her boyfriend, Aakash to Rajan and Madavi who looks exactly like Vyom.
Shivani convinces Rajan to live in the old Bedi house. Rajan was reluctant but Akaash in his stern voice confirms that what Shivani wants shall be done by which Rajan gets reminded of Vyom and his firmness. Shivani and Akaash plans for their engagement during which Shivani hears some strange spooky voice and feels some strange shadow behind her. At the engagement party, Akash surprises Shivani with her favorite superstar Krrish Khanna who looks exactly like Shiv. Then they meet Radhika at their film shooting who is Sharanya's lookalike.
Then, Suvarna reveals that not Shivani but Radhika is Sharanya's reincarnation and that Odhni and Suvarna swapped the babies because Rajan and Madhvi only adopted Shivani because they thought she was Sharanya's reincarnation. On knowing the truth by Suvarna, Rajan and Madhvi torchers her and chains her in the basement. There is always a shadow which is keeping a watch on all the actions taking place in Bedi house.
Accidentally KK sees an old lady (Survarna) chained and tries to rescue her but gets hurt from back. He tries to make everyone believe him that he have seen an old lady chained but none does. After few days Radhika hears a scream and follows seeing Rajan and Madhvi taking the same old lady ie; Suvarna and pushing her into a car. Radhika tries to make everyone believe her but none does. Kk later comes and convinces her that she is right and both plans to find out the secret behind it. Shivani then convinces Akash to get married but on the day of marriage, The groom turns out to be Old Vyom. It is revealed he was the shadow that was lurking around the house. Suvarna pushed him before he could be shot claiming it was his punishment. After that Shiv and Sharanya live happily life after