I don't know that you'll ever get it perfect, but you can get better results that may be usable depending on what you're working on.
I first amplified the file +12dB using the on-screen volume control. I then zoomed into the first 4 seconds of the file and selected the region from 0:00.00 to 0:00.8, which was just the camera buzz and hiss without any speech. I opened the Noise Reduction effect then exposed the Advanced section at the bottom. I changed the FFT Size to 512 (after a few tests with higher values, this sounded best) and clicked the Capture Noise Reduction button at the top.
I then removed the selection, by clicking in the waveform and adjusted these values:
Noise Reduction: 80%
Reduce By: 22dB
Spectral Decay Rate: 75%
Certainly not perfect, but the buzz is gone and the hiss is greatly reduced. The speech is audible and the reverberation artifacts are reduced. You can certainly play with these settings to find a happy medium between noise and warbly artifacts, though.
You've probably fixed your audio by now, but I've recently come across a few really bad situations on my end as well and have been experimenting with different clean up methods. I took a shot at cleaning yours up for more practice and followed much of the guidance offered by durin above. Completely eliminated the buzz-- still some echo and artifacts, but definitely listenable and could be negated further with an audio bed. Here's the file if it's helpful.