In this episode, Mr. Gold forces Hook to help him put a man (the Apprentice) inside the hat, while flashbacks show Rumplestiltskin's past encounter with Anna.
A long time ago, the Apprentice (Timothy Webber) is sweeping a vault, when an unknown Dark One intrudes, later revealed to be Zoso.
Anna (Elizabeth Lail) arrives at Rumplestiltskin's (Robert Carlyle) tower and talks to him about the disappearance of her parents.
Rumplestiltskin offers to help if she puts the contents of a vial into the Apprentice's drink telling her that he is an evil man.
Anna goes to the man's house and after a brief conversation she has a chance to put the vial's contents into his tea but instead decides to throw them into the fire thinking that it is poison.
Anna arrives back at Rumplestiltskin's tower and informs him that she gave the contents of the vial to the Apprentice.
They go to the cottage and Rumplestiltskin states he won't change the man back if they find him because he is protecting the box.
In order to open the box he needs magic from someone who faced their inner darkness and succeeded as he was planning on Anna not giving the antidote.
Anna says that she doesn't have inner darkness and Rumplestiltskin reminds her that due to the contract she will spend the rest of her life in his tower.
Anna refuses to accept this and holds a sword to Rumplestiltskin's heart, demanding him to rip up the contract.
Rumplestiltskin tells Anna that the King and Queen of Arendelle arrived on his doorstep seeking a way to take away Elsa's powers forever.
However, the Apprentice, now in the form of a mouse, jumps onto Rumplestiltskin's hand and bites him, causing him to drop the dagger.
Anna uses the dagger to force Rumplestiltskin to give her the box, and saying he will never harm either of the sisters and their family, as well as commanding him to turn the Apprentice back into his human form.
Back in Arendelle, Kristoff (Scott Michael Foster) is talking to Sven when all of a sudden, Anna appears.
Emma Swan (Jennifer Morrison) arrives at Granny's diner and asks Captain Hook (Colin O'Donoghue) out on a date.
The Charmings, David (Josh Dallas) and Mary Margaret (Ginnifer Goodwin), are shown helping Elsa at their loft by going through spell books.
Hook runs into a drunk Will Scarlet trying to break into the library and punches him in the face when Will refuses to stop.
Hook again is put off by his hand controlling his actions and tells Will that if he informs anyone of what happened he will be a dead man.
The Storybrooke version of the Apprentice answers the door and Mr. Gold tells Hook to force him into a chair.
Mr. Gold produces a video tape with a recording from the house they just left, threatening to reveal it to Emma.
David, going through documents with Elsa, tells Emma that the Snow Queen's alias, Sarah Fisher, is nowhere in any Storybrooke records stating that she did not arrive at the town via the curse.
In a review from Entertainment Weekly, Hilary Busis notes "If you spent the rest of the hour swooning, though, you may have missed out on the explication of a few crucial plot points.
As its name implies, "The Apprentice" focused on revealing why, exactly, Rumpelstiltskin was so tickled to discover that Sorcerer's hat in the house where he and Belle honeymooned in season 4's premiere.
As it turns out, the object is more than just a groovily decorated cap—it's also an artifact of immense power that could have enormous implications for the rest of our heroes.