Castle and Beckett continue to talk about their wedding preparations. They veto Martha's over the top flower arrangement ideas. Martha is not happy about that. Castle and Beckett head-off to a construction site wondering how to involve Martha in their wedding preparation.
A worker at a construction site has found the bones of a man. Castle sees the watch and the ring on the dead man and correctly identifies him as Vince Bianchi, the mobster who suddenly disappeared in 1978.
To find who killed Bianchi, Castle and Beckett visit the house of his close aide, Harold Leone. The man is still stuck in 1978 -- as he believes it is still the 1970s era -- and passes sexist comments, addressing Beckett as cup cake and refuses to see her as the person in charge of the investigation. Castle takes the lead and calls himself Captain Castle. When informed that they have found the body of Bianchi, Harold wants to see his body.
Lanie informs Castle and Beckett that Bianchi was shot at multiple times. She has made a mould of the murdered mobster, as the concrete poured on him made a perfect outline. The mould gets the proper paint on the face and hair on the head. The morgue gets the 1978 decor and Lanie is dressed-up as Foxy Brown. Harold sees the body and is convinced about his friend's death. He also sees his watch, ring and a coin. Harold tells Beckett and Castle that Bianchi always had the coin with him.
Soon, a man, who is dressed like a surgeon, opens fire at Harold. The man gets out of the building, without killing anyone. Afterwards, Harold tells that he will reveal who killed the Bianchi at the precinct. Castle suggests that they take Martha's help to transform the precinct and make it look like a precinct of 1978. Martha goes over the top and hires actors to make the whole set-up look authentic.
Esposito and Ryan appear at the precinct as the famous cop duo, Snookie and Ray, of the 1970s. Harold recognises them. They try to make him talk about who may have killed Bianchi. Harold gets confused when he hears Esposito's cell phone ring. He wants to visit Glitterati, the nightclub of the 1978. Bianchi used to frequent that nightclub. Ryan and Esposito find that the nightclub has been re-opened as the 1970s club. They take him to the club.
While Beckett is questioning the man who opened fire at Harold, Castle discovers that the night Bianchi was killed, he was at Glitterati, which was -- and is still -- owned by one of Bianchi's rivals, Frank Russo.
Harold sneaks-up to Russo's office and pulls out a gun at him. He wants him to confess that he had killed Bianchi. Esposito and Ryan stop him from shooting at Russo. Harold was pretending to be muddled and stuck in 1970s. Beckett and team find a coin, similar to the one found on Bianchi, with Harold. Beckett accuses him of killing Bianchi out of jealousy.
Harold confesses that he and Bianchi were lovers. But, he had asked him to marry a woman and have a family, as the outing of their relationship would have caused trouble.
The real murderer turns out to be Russo's wife and sister of Michael Carcano, one of the rivals of Bianchi. Bianchi and Carcano had decided to become a family. Bianchi was expected to marry Carcano's sister. He had gone to see her at the Glitterati and when he had refused to marry her, she had shot at him, multiple times.
Beckett tells Harold that Bianchi loved him a lot and that is why he refused to get married. The Castle gang and Harold head to Gliterrati and groove to disco era music.