Kristin Lehman, Louis Ferreira. Brendan Penny

It's not a whodunit, it's a whydunit! ABC's Motive returns for its sophomore season on Wednesday, May 21 (10/9c), doing what most crime shows wouldn't dare: The killer is revealed in the opening moments of each episode.

"It's so much more compelling than having eight suspects," says Dennis Heaton, showrunner of the Canadian import series. "When things happen in life — whether it's something as tragic as a death or as trivial as a parking ticket — one of our most important questions is: 'Why did this happen?'" The concept, says Heaton, "pushes all of us to up our game in terms of how we approach mystery writing. Every episode of Motive is a Rubik's Cube."

Expect a seismic shakeup this season with the introduction of Sgt Mark Cross (Warren Christie), a golden boy fresh from a two-year human-trafficking case that made big headlines. "Cross creates good press so, as his reward, he's promoted to homicide," Heaton says. "We soon find out that he and Det. Angie Flynn [Kristin Lehman] have a past she wishes would stay buried." The ripples will be huge — on the department and on Angie's relationship with Det. Oscar Vega (Louis Ferreira).

"Cross intends to integrate himself into the cases and put his stamp on everything," Heaton says. "For Angie and Vega — two seasoned professionals — that's very disconcerting."

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