‘Murder 3’ opens with Vikram (RandeepHooda), a hot-shot fashion and wildlife photographer, viewing a video of his girlfriend, Roshni (Aditi Rao Hydari) telling him she is leaving him. Vikram becomes distraught. While drinking away his sorrows at a bar, he meets Nisha (Sara Loren) and they have a relationship where Nisha moves into the house that Vikram was sharing with Roshni. Vikram becomes a suspect in the disappearance of Roshni, however, the investigators can find no evidence of Vikram's involvement in Roshni's disappearance.

It is revealed that the house is owned by a German lady who shows Roshni a secret room built to hide her husband just in case someone came to look for him because he was in British Army at the time of 1947. In a flashback, it is also shown that Roshni, jealous of Vikram's relationship with one of his colleague, decided to pretend she is leaving him. She creates the video saying she is leaving as she hides in the secret room. The room has some one way mirrors where she can observe Vikram's reaction. When she decides he has had enough she looks for the key and realizes she lost the key and is now trapped in the room with no way to contact him.

Nisha finds the key to the secret room, but she doesn't know what it is used for. Nisha eventually figures out that Roshni is trapped in the house because Roshni is able to communicate through tapping on the pipes in the secret room. As Nisha is ready to open the door, she pauses and decides not to rescue Roshni because she might lose Vikram after that. Nisha struggles with her decision, but decides to open the door and check on Roshni because the investigators gave Nisha pictures of Vikram and his Colleague and she herself feels the pangs of jealousy. As Nisha is checking on Roshni laying in a bed in the secret room, Roshni surprises Nisha and knocks her out with a glass bottle and leaves Nisha locked in the room.

After Roshni comes out of the secret room, she sees Vikram and his colleagues photographs and shatters. She decides to leave the house. She leaves that picture of Vikram with his colleague on mirror and also sticks her necklace to show Vikram that she is out and then she sends the keys of the room to the investigator who actually loves Nisha. The investigator comes and arrests Vikram. The final scene shows Roshni tearing her and Vikram's photograph and is going on a highway road in a car alone, happy on leaving the devastated and arrested Vikram.