Sarah came into his lab, used Eldrad's ring to render Carter unconscious and took the hand. When he woke, he drove the Doctor to Nunton Experimental Complex in pursuit of Sarah.
The use of the ring on Carter brought him under Eldrad's influence — in Sarah's words he had "seen the light of Kastria". In an attempt to prevent the Doctor from reaching Sarah, Carter attacked him, but his own momentum saw him fall several storeys down inside the complex to his death. (TV: The Hand of Fear)