By Ariana Bacle
September 27, 2017 at 01:49 PM EDT

Joanne Froggatt experienced no shortage of horrors playing Anna Bates on Downton Abbey — but while those were cloaked in a prim, historical drama, her latest show is a full-on thriller that revolves around one date between Froggatt’s character, a schoolteacher, and surgeon Andrew (Ioan Gruffudd).

“As most thrillers go, it’s not a happy event that happens,” Froggatt laughs. “They go out on a date and events occur that evening that they’re both involved in, and they both have very differing opinions of what happened during that night,” she explains. “As the title would suggest, it becomes very much a psychological thriller with a strong theme of lying and who’s lying and who is telling the truth, and the audience has to figure out — along with the other characters in the story — who is telling the truth?”

Aside from voicing a character on Bob the Builder, this marks Froggatt’s first major TV role since Downton Abbey ended in 2015. She won a Golden Globe and nabbed three Emmy nominations for her performance on the beloved period drama.

“I had never done a thriller before,” Froggatt says. “It’s very cool, it’s very cinematic. It’s very difficult to find something that feels original, whether it’s a story or a production, and I felt this was.”

Joss Barratt/Sundance TV

Plus, there were experts at the helm: Brothers Harry and Jack Williams created Liar after previously pairing up on BBC One’s Emmy-nominated The Missing, a mystery about missing children. The duo tell EW they wanted to do something “a little more linear” after two seasons of The Missing. 

“I would say, tonally, it’s different,” Harry says. “But it does have those twists and those turns and surprises along the way.”

And although the six-episode season is full of those twists and turns, Froggatt promises it all ends with a “satisfying conclusion.” “It’s definitely a thriller that you can watch and get to the end and feel like you can pay back for your investment and time and emotion into this story,” she teases. “It’s not something that’s too open-ended — it’s a whole story, and a real roller coaster of a story.” Adds Jack: “You’ll get hooked.” And he wouldn’t lie, would he?

Liar premieres Wednesday at 10 p.m. ET on Sundance.