Trefusis

Miss Trefusis was head prison guard of Broadfell Prison, which held Lucy Saxon, as well as a member of a cult that worshiped Harold Saxon. (TV: The End of Time)

Trefusis knew about and was sent to collect his ring. (TV: Last of the Time Lords) The governor, several guards and she resurrected the Master. The Master took her life energy, killing her, as well as that of several prison staff. (TV: The End of Time)