In the context of the popular crime drama Criminal Minds , the "piece" usually refers to the physical puzzle pieces sent by the unsub Randall Garner—the Fisher King—to the BAU team.
A man suffering from Capgras Syndrome (believing his loved ones have been replaced by imposters) after a traumatic brain injury. [S7E3] The Fisher King
Spencer Reid is cast as "Sir Percival" and is given the task of asking the question that will "heal" the King. Context for S7E3: " Dorado Falls " In the context of the popular crime drama
The "piece" for the puzzle was a section of a large map or picture that, when assembled, revealed the location of his "Grail"—his daughter, Rebecca. [S7E3] The Fisher King