Benanti will play Renata Ellard, the fiancee of Colin Sweeney (Dylan Baker), an accused wife killer and frequent Lockhart/Gardner client.
Here's how the episode is billed: "When Alicia pays a visit to longtime client Colin Sweeney, she finds herself in the unwanted role of witness when a body is discovered in his home. Meanwhile, Eli steps in when an unfortunate picture of Zach threatens to become a public relations nightmare for Peter."
Josh Charles directs the episode, which airs from 9-10 PM ET.
Benanti received Tony Award nominations for her work in Swing!, Into the Woods and Women on the Verge of a Nervous Breakdown and won Best Featured Actress in a Musical Tony for her performance in Gypsy. Her stage work also includes Nine, The Wedding Singer and In the Next Room.
Her TV work includes "The Playboy Club," "Law & Order: SVU," "Royal Pains" and "Go On." She recently played Elsa Schrader on NBC's The Sound of Music Live!