A teaser trailer for “Room,” Brie Larson’s first starring vehicle since “Short Term 12,” now has a teaser trailer.

An adaptation of Emma Donoghue’s best-seller, “Room” finds a young mother (Larson) and her five-year-old son fleeing the small shed they’ve been trapped in for the past half-decade. (Though the trailer doesn’t make this clear, little Jack’s father is his mother’s kidnapper.) Jack has never known the outside world, so it’s up to “Ma” to reveal it to him.

The novel is written from Jack’s point of view, but the trailer focuses on Larson’s character. Donoghue also penned the script, in what seems to be an increasing trend of authors adapting their own works for the screen.

Joan Allen, Megan Park and Kate Drummond co-star.

No release has yet been set, but the film will make its Canadian debut at the Toronto International Film Festival next month.