Readers assume that commonplace properties of the real world also hold in realistic fiction. They believe, for example, that the usual physical laws continue to apply. But controversy exists in theories of fiction about whether real "individuals" exist in the story's world. Does Queen Victoria exist in the world of "Jane Eyre," even though Victoria is not mentioned in it? The experiments we report here find that when participants are prompted to consider the world of a fictional individual ("Consider the world of Jane Eyre . . ."), they are willing to say that a real individual (e.g., Queen Victoria) can exist in the same world. But when participants are prompted to consider the world of a real individual, they are less willing to say that a fictional individual can exist in that world. The asymmetry occurs when we ask participants both if a real person is in the character's world and if the person "would" appear there. However, the effect is subject to spatial and temporal constraints. When the person and the character share spatial and temporal settings, interchange is more likely to occur. These results shed light on the author's implicit contract with the reader, which can license the reader to augment a fictional world with features that the author only implicates as part of the work's background. [This is the online first version of an article published in "Psychonomic Bulletin & Review."]