red herring

In the mystery novel A Study in Scarlet, the detective Sherlock Holmes examines a clue which is later revealed to be intentionally misleading.

A red herring is something that misleads or distracts from a relevant or important question. It may be either a logical fallacy or a literary device that leads readers or audiences toward a false conclusion. A red herring may be used intentionally, as in mystery fiction or as part of rhetorical strategies (e.g., in politics), or may be used in argumentation inadvertently.