Isabella Margaret Beavis was a CSIRO employee who attended the Nashes' New Year's Eve party in Chatswood. Other than Dr Bogle, she was the only guest not to attend with a partner.

She was the third person to give evidence on the first day of the inquest proper, on 7 May 1963. She gave evidence about timings and told the court how she had left the party at about the same time as Dr Bogle, at about 4am:

Beavis: I heard the sound of a car engine starting when I got into my car. I looked to the opposite side of the road and saw Dr Bogle in a car. He waved and tooted the horn and then drove past the front of the house. I went in the opposite direction.