Walter Mitty (Ben Stiller) is a film printing manager who has worked at Life magazine for 16 years. He is introverted and can't even talk to his favorite colleague Cheryl (Kristen Wiig). Facing life, he is like a bystander, often "emptying" his daydreams. Until one day the company was acquired and the magazine needed to make the cover of the last issue. The key to the success of the cover is to find a roll of film from the wild photographer Sean (Sean Penn). Walter finally talked to Cheryl and embarked on a real adventure with the encouragement of her and her mother (Shirley MacLaine). The ice field, the sea, the Himalayas... Walter's daydreams are far less magnificent than reality.