Beyonce Knowles, Ali Larter and Idris Elba will star in “Obsessed,” a thriller that Screen Gems will put into production this summer. Steve Shill will direct a script by David Loughery. Will Packer produces, and Knowles will be exec producer along with her father, Mathew Knowles. Screen Gems topper Clint Culpepper is finalizing cast deals, working with Knowles’ and Larter’s reps to iron out scheduling kinks. Knowles is also producing and co-starring as Etta James in “Cadillac Records” for Sony BMG; Larter is working on episodes of NBC’s “Heroes. “In “Obsessed,” Elba will play an asset manager who has a knockout wife (Knowles) and thriving career until a temp office worker (Larter) begins stalking him. Knowles was last seen onscreen in “Dreamgirls,” Larter in the Screen Gems films “Resident Evil: Extinction” and “Final Destination,” and Elba last appeared in “American Gangster.” He next stars in “Prom Night” for Screen Gems.