Allison Janney to guest on 'In Plain Sight'

Rita Moreno, Steven Weber also set appearances

It's shaping up to be a busy winter for Allison Janney.

The "West Wing" alumna, who recently booked a co-starring role opposite Matthew Perry on ABC's comedy pilot "Mr. Sunshine" and a pivotal recurring role opposite William H. Macy on Showtime's drama pilot "Shameless," is set to guest star on USA Network's drama series "In Plain Sight."

In a two-episode stint, she will play a newly-appointed US Marshal for the district who butts heads with Mary (Mary McCormack).

Also set to guest star on the upcoming third season of "In Plain Sight" are Rita Moreno, Steven Weber, Tess Harper and Josh Cooke.

Moreno will play Raph's (Cristian de la Fuente) aunt Rita who takes the town by storm, helping Mary and Raph plan their wedding.

In two episodes, Weber will play a brilliant and charming FBI agent who has different point of view on the handling of federal witnesses.

Harper will appear as a take-no-prisoners Federal Prosecutor who thinks a win in court is the most important thing -- despite the personal costs to a witness.

And Cooke plays in the role of the very first witness of Mary and Marshall's (Frederick Weller) first case together.

Season 3 of "IPS" premieres March 31 on a new night, Wednesday.