Complex sentence: Alastair is eventually set free of his bonds by an unseen force and seizes the opportunity to attack Dean and Castiel, but is incapacitated and tortured by Sam, who forces him to admit that demons are not involved in the angel murders.
Split into simpler sentences: Alastair is eventually set free of his bonds by an unseen force. He seizes the opportunity to attack Dean and Castiel, but is incapacitated and tortured by Sam, who forces him to admit that demons are not involved in the angel murders.