Digital Game-based Learning (DGBL) has achieved several positive results in recent years, e.g., increased fun, motivation, or learning outcome. However, many DGBL applications fail, which makes an isolated consideration of individual game elements and their influence on learning necessary to better design future DGBL applications. One widely used game element is the game story. As there is little research on how a game story should be designed to promote learning, this paper conducts an experiment comparing a fictional game story with a realistic one. The results show that both game stories lead to a significant objective knowledge gain. In terms of learning outcome, both game stories achieved similar results.