“What if he never left? What if we locked him out here with us?”

The "he" and "him" in question is the terrifying, world destruction-bent monster of "Stranger Things." In Netflix's new trailer for Season 3, Eleven (Millie Bobby Brown) is adamant that she closed the door to the Upside Down's other dimension. But Will (Noah Schnapp) senses the monster is still with them — and he's looking for a new host.

That host seems to be Billy (Dacre Montgomery), who ominously promises to "end everyone."

Also returning for Season 3 are Winona Ryder, David Harbour, Finn Wolfhard, Gaten Matarazzo, Caleb McLaughlin, Sadie Sink, Natalia Dyer, Charlie Heaton, Joe Keery, Cara Buono and Priah Ferguson.

Joining the cast this season are Cary Elwes as Hawkins' mayor; Jake Busey as a local reporter; and Maya Hawke as an employee at the new Starcourt Mall's ice cream shop.

"Stranger Things" Season 3 premieres July 4 on Netflix.