The Inquisitor - S1.E18

When a college friend of Rebecca's, Amateratsu, and her grandfather Kajimori travel to Paris, the grandfather is kidnapped by the Inquisitor, a member of the League of Darkness. Kajimori has knowledge of a potion of "enlightenment," which he has passed on to Amateratsu. Amateratsu and Jules have become involved, and the League go after her when Kajimori tells them nothing. Rebecca and Phileas become involved when the two are kidnapped. Amateratsu gives her grandfather the potion, and he uses it to destroy the Inquisitor by showing him the "light" before himself disappearing.