Frank Paxton

 was a member of a team that was due to spend a year at Hardy Base to work on the cyclotron. He brought his saxophone with him.

However, Frank was part of a terrorist group that attacked the base. He killed Madeleine, but Catherine escaped into the cyclotron before he could kill her. After she was brought out of the cyclotron by the Fifth Doctor, the Doctor hit Frank with the saxophone and they escaped in the TARDIS. (PROSE: Lackaday Express)