The truth may drown them all.

What happened to Percy? The answer threatens to drown not just Bill Pullman's Det. Harry Ambrose but everyone on Hanover Island.

The new trailer for The Sinner season 4 sets the stage for the series' next mystery, and it all starts when Harry spots a woman walking off a cliff by the ocean. This woman is Percy Muldoon (Alice Kremelberg), the daughter of an affluent family on the island.

Authorities drag the surrounding waters but can't find signs of a body. In fact, a witness claims to have seen Percy drive away after Harry's initial 911 call, forcing him to question whether he actually saw what he thinks he saw. Meg (Frances Fisher), the Muldoon family matriarch, doesn't believe Percy would've killed herself. And maybe she didn't.

Harry later learns Percy was afraid a man was after her. On a boat, he finds a message carved in the wood that appears to read, "Free the flesh from the bone." Meg also seems to know more than she's letting on. "You need to let this go," she tells Harry. The trailer warns that, whatever the truth may be, Percy's "sins will drown them all."

Jessica Biel, who starred in the first season of The Sinner, returns as an executive producer on the eight-episode fourth season alongside showrunner Derek Simonds.

Jessica Hecht returns as Harry's partner, Sonya, joining the new cast of Michael Mosley (Colin Muldoon), Neal Huff (Sean Muldoon), Cindy Cheung (Stephanie Lam), and Ronin Wong (Mike Lam).

The Sinner season 4 premieres Wednesday, Oct. 13, at 10 p.m. ET/PT on USA Network.

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