In the upcoming Winter Finale of “Quantico,” the people responsible for the bombing of Grand Central Station will be revealed.

A teaser for Episode 11 of Season 1, titled "Inside," shows Alex (Priyanka Chopra) starting to panic as she explains the person behind the tragedy must be coming from inside the FBI.

“Whatever the FBI is doing, it’s not enough,” she says. “The real bomber is inside the bureau.”

The pressure is on for Alex, who has plead guilty to a crime she did not commit. If the FBI does not find the real bomber within 48 hours, she will be serving a life sentence.

“Desperate Housewives” actress Marcia Cross will be making her big return to ABC in the upcoming episode. Cross will be playing Caleb's (Graham Rogers) politician mother, Senator Claire Haas.

The character has been teased along throughout the season, and will be revealed to have some seriously dark motives.

A clip shows Haas being introduced to her son’s date Hannah Wyland (Eliza Coupe) at a Christmas party. The holiday party small talk quickly turns towards the subject of terrorism when Hannah starts to extoll the senator’s heroic actions on 9/11.

"We lost too much that day," says Haas. "Each and every one of us."

Claire Haas has been built up over the season as a very powerful figure who has made the transition from decorated FBI agent to a senator with aspirations toward the vice presidency.

Although the public views her as highly skilled politician with her heart in the right place, her family sees her as an ambitious schemer who is capable of doing anything to get what she wants.

The Winter Finale of “Quantico” airs Sunday, Dec. 13 on ABC.