Future Imperfect

"Future Imperfect" is the 82nd episode of the science fiction television series Star Trek: The Next Generation. It is the eighth episode of the fourth season. During an away mission on Alpha Onias II, Riker falls unconscious and awakens to discover that sixteen years have passed. He's told that he's now captain of the Enterprise, and that Picard is a Starfleet admiral who travels in a Romulan warbird. Doctor Crusher explains that a long dormant virus in Riker's system recently became activated and destroyed his memories of everything that transpired in his life during the past decade and a half. Riker thinks this is a Romulan charade, but the truth is stranger than that.