Exclusive: First Footage of Ben Affleck in 'Gone Girl'

First footage from David Fincher's highly anticipated 'Gone Girl.'

ET has your first look at footage from David Fincher's feverishly anticipated Gone Girl!

Based on Gillian Flynn's bestseller, the film revolves around the complicated marriage of Nick Dunne (Ben Affleck) and his wife Amy (Rosamund Pike), who's gone missing on their fifth wedding anniversary. And before long, under police pressure and a growing media frenzy, Nick's dark behavior begins to emerge.

Video: Ben Affleck -- Hollywood's Golden Boy

... But could he really have killed his wife?

Click the video for a teaser from the film's full, uninterrupted trailer set to debut Monday on ET, which shows a much darker side of Affleck than audiences are used to.

Related: First Look at Ben Affleck in Fincher's 'Gone Girl'

Gone Girl hits theaters October 3.