Castle (Nathan Fillion), a murderer? All of the signs were pointing to one very creepy yes as the team began to doubt their mystery novelist colleague, which made for a seriously gripping episode. Especially since Beckett (Stana Katic) and Castle’s fledgling relationship was also caught in the killer’s twisted crosshairs. In this case, "gripping" equated to absolute brilliance. Do you agree? Weigh in below!