In the 18th episode of season 11 of Criminal Minds titled "Derek," a dramatic farewell takes place between two main characters, Derek Morgan and Spencer Reid. The episode starts with the team investigating a series of escalated home invasions, but things take an emotional turn when Derek announces his departure from the team.

Derek, portrayed by Shemar Moore, explains to the team that he is leaving to focus on his family and start a new chapter in his life. Spencer, played by Matthew Gray Gubler, is deeply affected by this news as he considers Derek to be a mentor and father figure. Throughout the series, the bond between these two characters has been evident, making this departure all the more impactful.

As the episode progresses, viewers witness heart-wrenching moments between Derek and Spencer as they share their fondest memories and express their deep appreciation for one another. Their farewell scene is particularly moving, leaving fans in tears as Derek walks away, leaving behind a devastated Spencer.

The episode concludes with the team coming together to solve the case, displaying their resilience and determination in the face of adversity. However, the loss of Derek will undoubtedly have a lasting impact on the team dynamics.

Overall, "Derek" is a bittersweet episode that marks the end of an era for Criminal Minds. It showcases the enduring friendship between Derek and Spencer, leaving fans with a sense of loss and anticipation for what lies ahead for the remaining team members.