Brit actor Dan Stevens couldn't have picked a better vehicle to explode his proper image as Matthew Crawley on Downton Abbey. In The Guest, Stevens plays David, a U.S. soldier who intros himself to a family in New Mexico as the BFF of their son, who was killed in Iraq. He's not what he seems. Cue the psycho rampage. It's hellish good fun. Stevens is mesmerizing as the avenger, helping director Adam Wingard turn The Guest into a blast of wicked mirth and malice.