Masters was the Permanant Under-Secretary at the Ministry of Defence, a civil servant. He paid a visit to the Wenley Moor nuclear research facility when a series of power drains and mental breakdowns happened. In reality the Silurians had tampered around with the nuclear energy and this was causing infections. During his visit, the station security chief Major Baker was infected. Masters left before the base was quarantined unaware of himself being infected.
Masters reached London eluding search parties looking for him, and was caught by two police officers on a bridge. Masters then slumped and died from the virus. (DW: Doctor Who and the Silurians)