There are two big unknowns in Castle. The murderer of Beckett's mother... and Rick Castle's father. What if both were identical?
I literally can see it in front of me: In the last episodes of season 4, Castle finds out about his long missed father. After a awkward start and some serious trouble with Martha, little Ricky and his new dad come along very well. They smoke cigars together, have some deep talks. But in the last episode of the season, Castle finds some disturbing detail's about his father's past. And Beckett finds a new hint to solve her life's trauma. Push comes to shovel and in the last scene of season 4 Becket is standing with a gun pointing at the killer. Castle comes in and has to decide: should he let Beckett kill his father? He stands in the line of fire to protect his father. But the father has a gun, too. Becket shouts: "Castle, down!" We hear two shots. And...cut.



