The overarching storyline of Quantico will finally be given resolution on its upcoming midseason finale. The episode, which promises to reveal the identity of the attackers, will air on Sunday, Dec. 13th. Meanwhile, the FBI thriller has added three new faces to join its freshman season to be part of the NATs.

Quantico fans should mark their calendars for the midseason finale of the series, as it will finally answer one of this season’s burning questions: “Who is responsible for the deadly attack in Grand Central Station?” However, while the one-hour episode promises to satisfy our curiosity, more questions will follow as events progress.

Details about the episode titled “Inside” have been shared by The Futon Critic.

In flashbacks, the NATs will find themselves receiving a few days off for the holiday break. Although this sounds like a great time to relax, viewers will be exposed into some secrets for some of the major players.

“Inside” will also feature the debut appearances of Marcia Cross as Claire Haas and Eliza Coupe as Hannah Wyland.

As for the show’s ratings, it appears that Quantico hasn’t been performing strongly in the past weeks. According to TV Series Finale, there had been a huge slip from the ratings as well as total viewership since ABC aired the pilot.

Its most recent outing, which aired on Nov. 15, targeted a total of 4.2 million viewers and a 1.33 rating. It marked a slight dip from its Nov. 8th installment that was watched by 4.3 million viewers.

In other news, the Priyanka Chopra-starred drama has added three new actors on its first season cast. This includes: Jay Armstrong (Sex and The City), Lenny Platt (How To Get Away With Murder) and Li Jun Li (Minority Report). Entertainment Weekly has learned the casting news on Tuesday.

Johnson will play Will Olsen, a socially awkward NAT who got his Ph.D. from Harvard at age 22. Platt, meanwhile, will play Drew Perales, a charming retired NFL player who fought a class-action lawsuit in the past. Lastly, Li will play Iris Chang, a rich and queen-bee type of NAT who comes from a wealthy family.

The incoming trio has booked multi-episodes when the show returns with new episodes in March.

Quantico airs Sundays at 10 p.m. ET on ABC, with its midseason finale airing Dec. 13.