Ted Rollins is found shot to death in his bathtub but his body was moved from Coney Island. 

Rollins was a computer hacker and his online activity lead Beckett and Castle to Anderson Cross, who is really Jackson Hunt, Castle's father. Hunt tells Castle not to tell Beckett the truth.

Later, the team suspects that Cross is a former CIA operative turned assassin. When Hunt turns up shot on Castle's doorstep and needing help from Rick and Martha, Rick ends up telling Kate everything.

Jackson claims he's deep undercover and must stop a CIA mole. He enlists Kate and Rick's help.

Later it appears he's set them up as bait to draw out the mole, whom he kills in cold blood in front of Castle. When Rick goes to get Kate, they return to find the man's body missing and Jackson has disappeared. 

Castle tells Kate that he's been wrong to think of Hunt as his family. She's his family and they set September as their wedding date.