After a long and eventful life, Allan Karlsson ends up in a nursing home, believing it to be his last stop. The only problem is that he's still in good health, and one day, he turns 100. A big celebration is in the works, but Allan really isn't interested (and he'd like a bit more control over his alcohol consumption). So he decides to escape. He climbs out the window in his slippers and embarks on a hilarious and entirely unexpected journey. It would be the adventure of a lifetime for anyone else, but Allan has a larger-than-life backstory: Not only has he witnessed some of the most important events of the twentieth century, he has actually played a key role in them.