As is too often her wont, Hannah Ware is running late. “I’m on the way to the airport,” the British actress, 31, tells me breathlessly. She’s off to Greece, where her little sister, the pop star Jessie Ware, is going to be married. “I got demoted from maid of honor,” she admits. “I guess my sister doesn’t trust me with, you know, important things.”

In all fairness, Ware has played pretty untrustworthy types in her two breakout TV roles. On Starz’s Boss, as the troubled daughter of Kelsey Grammer’s politico, she struggled to keep her drug addiction under wraps. In the recent ABC series Betrayal, her character’s infidelity is the focus of the show. “I’m no good with a lot of things—directions, timing—but I’m quite good with secrets,” she promises, right before offering up another confession: “I’m doing something incredibly naughty. I’m making the back of my bridesmaid dress lower than it should be—like, Rihanna style—but my sister doesn’t know it yet.” She laughs heartily. “That’s awful, isn’t it? This is why she doesn’t trust me.”

Although she made brief appearances in Spike Lee’s 2013 Oldboy and Steve McQueen’s 2011 Shame—a sex-addiction drama in which, Ware jokes, “my ass did the acting”—her role in the upcoming action movie Agent 47 could be her moment to shine on the big screen. Suddenly, she is keeping her lips sealed. Asked about her character, Ware’s answer is poetically— and contractually—vague: “I learn I am not who I think I am.”