When "Castle" returns, an upcoming episode will see Beckett go undercover.

Beckett (Stana Katic) will be involved in an undercover operation in an upcoming episode that delves into her backstory. However, the mission will get increasingly complicated.

"Beckett thinks she's pretending to be one person, but discovers that [the criminals] think that she's somebody else completely," showrunner Andrew W. Marlowe told TVGuide. "She has to navigate those waters and figure out who she's supposed to be, and any misstep could get her killed."

As the undercover operation becomes compromised, Beckett will come into contact with some familiar characters from the Johanna Beckett murder investigation.

On the episode before "Castle's" brief hiatus, Beckett discovered her perfect wedding dress while investigating a high-fashion murder.

In "Dressed to Kill," two fashion students are digging through a dumpster for fabric when they discover a dead body. It turns out the deceased woman is named Ella, a former assistant of Matilda King (guest star Francis Fisher), a tough, Anna Wintour-esque fashion editor.

Esposito (Jon Huertas) and Ryan (Seamus Dever) speak to the victim's roommate, who says Ella did not have a social life because she was always on call for Matilda. Beckett and Castle (Nathan Fillion) go to interview Matilda King at the fashion magazine. It turns out that Matilda knew Kate when Kate was a young model who turned down a big photo shoot.

Matilda had fired Ella the day before her murder after she made scheduling mistakes. Matilda also fired her other assistant, Grace, because of Ella's mistakes. Photos show Grace and Ella fighting outside the building.

The team interviews Grace, and she says she feels like her fashion career is over because of Ella. Grace says that she saw Ella arguing with a man, and that he was threatening her.

Ryan and Esposito then discover a bug in Ella's apartment.

It's discovered that the man who was seen arguing with Ella is Mr. Conway, a lawyer who works for a rival fashion magazine. Conway says they approached Ella to spy for them, but she refused. But he said that she contacted him the night of her death, saying she had information about her magazine that she wanted to disclose.

When Ella phoned Conway, someone from her magazine heard the conversation. The person who overheard the conversation planted the bug in her apartment, which was ordered by Matilda King.

It's later discovered that someone outside the magazine had been changing Ella's appointments, seemingly setting her up. They find out that a designer named Yumi was changing Matilda's calendar. It turns out Yumi had stolen Ella's designs, then used a worker from Matilda King's fashion magazine to strangle Ella with a scarf.

Meanwhile, Matilda gives Beckett her perfect wedding dress, and the pair find a great venue for their wedding, which they decide will be in the spring.

On the next episode, "Smells Like Teen Spirit," "Castle and Beckett investigate the death of a mean high school girl at one of Castle's alma maters. Castle is thrilled when he discovers that it might be the work of a teenage telekinetic."

EP Marlowe said the next episode "takes us in that Carrie kind of world."

"Smells Like Teen Spirit" airs Monday, Feb. 17 at 10 p.m. EST on ABC.