You can watch the full episode on platforms like Apple TV or IMDb to see the mystery unfold. "Castle" G.D.S. (TV Episode 2016) - IMDb

If you are looking for a story inspired by the "helpful" or "contingency" themes of that episode, here is a narrative focusing on the lessons learned: The Secret Guardian

Sometimes being "helpful" means taking on a burden so others don't have to. Castle chose to live with a hole in his memory to ensure Beckett’s safety.