+1 (also known as Plus One and Shadow Walkers) is a 2013 American science fiction horror film directed by Dennis Iliadis and starring Ashley Hinshaw, Rhys Wakefield, and Natalie Hall. The film is about four college students, David, Jill, Teddy, and Allison, who attend a party. When the party is set back in time an hour into the past, there is a duplicate of every single person in the party doing what they were doing an hour ago. The plot revolves around the characters' unique actions.

Dennis Iliadis and Bill Gullo wrote the script after Dennis asked himself three questions. He hired Lola Visual Effects to edit the film and introduce the duplicate effect at the end of the film. It was done using computer-generated animation, LED displays, actors, and footage editing. The film first premiered at the South by Southwest film festival on March 10, 2013. On July 27, 2013, IFC Films acquired the U.S. rights to +1. On January 14, 2014, IFC released the film on DVD for the first time.