The Disciples of Saxon were a cult who worshipped the Master, who also went by "Harold Saxon". The Governor of Broadfell Prison and Miss Trefusis were known members of the cult, which appeared to be exclusively female.
The cult resurrected the Master with the aid of the Potion of Life as he had instructed them to do should he be killed. (TV: The End of Time) After his funeral pyre burnt down, Miss Trefusis collected the Master's ring, which survived unscathed. (TV: Last of the Time Lords)
The resurrection was interfered with because contacts of Lucy Saxon's family had calculated an opposing potion to the Potion of Life in preparation for the Master's predicted return. Lucy used it and sacrificed herself, blowing up Broadfell Prison. She and all the disciples were killed, although the Master survived. (TV: The End of Time)