The temporary alliances in both the ’90s and the present appear to be crumbling, and several characters are brandishing knives in the Season 3 trailer for “Yellowjackets,” which Showtime released Wednesday.

As the two-minute clip opens, we hear an ominous voiceover from Shauna (Melanie Lynskey): “The only way to be safe is to be the only one left.” A Drowning Pool song, “Bodies,” plays in the background, featuring the lyrics “let the bodies hit the floor.”

The trailer also features Lynskey saying, “Someone wants us dead,” after receiving a package with the mysterious symbol on it from the wilderness. So who’s behind the package? The 40-something Van (Lauren Ambrose) darkly notes, “The only people who know about this are us. Or dead.”

“People are willing to do some messed-up stuff, just to see another day,” says Melissa (Jenna Burgess) in the plane crash timeline. Meanwhile, Shauna (Sophie Nélisse) and...