Rita never explicitly finds out the truth about Dexter's secret life as a serial killer in the show. Throughout the series, Rita remains unaware of Dexter's double life. Tragically, she is killed in the season 4 finale ("The Getaway," episode 12) without ever discovering Dexter's true nature. In this episode, Dexter returns home to find Rita dead in the bathtub, having been killed by Arthur Mitchell, the Trinity Killer, before she could learn the truth about him.
