The Karlsson Brothers is a "confusion" comedy about two identical-twin brothers, each initially unaware of the other's existence. One brother is a successful, perfectionist lawyer living in Stockholm. The other brother lives in the North of Sweden with a wife and children, and is a notoriously unfaithful ne'er-do-well. The brothers meet for the first time as they go through their deceased mother's estate. Their meeting leads to a series of challenging mix-ups, turning both their lives on end. The brothers' differences prove gradually to be a source of strength, and their newfound friendship will change their lives forever.