11/12/2013 08:04 GMT | Updated 11/12/2013 08:06 GMT

WATCH: 'The Secret Life Of Walter Mitty' Exclusive Clip

In his secret life, Walter Mitty (Ben Stiller) dreams big... really, really big. There's no challenge beyond his grasp, be it climbing a massive glacier or rescuing a senior citizen from an exploding building. When he's not daydreaming, the not-so-secret life of Walter Mitty is the opposite of his heroic alter-ego's; he's just an everyday guy facing imminent career downsizing, who's too timid to ask out his pretty co-worker (Kristen Wiig). But when Walter faces his ultimate real-world test, he springs into action on a global adventure exceeding anything even he could have dreamed of.

'The Secret Life Of Walter Mitty' is in UK cinemas on 26 December. Watch our EXCLUSIVE CLIP BELOW...